54.12
Bulkhead Module
General Information
General Information
The Bulkhead Module (BHM) is the primary module
of the M2 electrical system. The BHM controls the
operation of the other multiplex modules in the system
along with a variety of other vehicle components either
directly or indirectly.
The Bulkhead Module is mounted on the cab side of
the frontwall and extends through an opening in the
frontwall into the engine side of the frontwall. The BHM
is located slightly below and outboard of the steering
column.
The BHM has four harness connections on the engine
side of the frontwall and three harness connections on
the cab side. Connections on the engine side include:
• forward chassis harness
responding to any inputs and all other power down
requirements are met.
To check whether or not the electrical system is going
into a sleep state:
1. Enter the vehicle.
2. Shut the doors.
3. Remove your foot from the service brake.
4. Make sure the ignition switch and hazard switch
are in the off position.
NOTE: One minute after these conditions are met, and
provided that one of the parameters in Table 1 has not
been added to the BHM, the odometer reading should
disappear. If the odometer reading does not disappear,
the electrical system is not going to sleep.
• engine harness
• two frontwall harnesses
Connections on the cab side include up to three dash
harness connectors.
Parameters
Parameter
Part Number
Description
Hours
26-01017-002
Switched Center Pin Power
For more information about the M2 electrical system,
see Section 54.00 "Electrical System."
26-01019-003
Exterior Lighting
16,667
24
26-01019-004
Exterior Lighting
16,667
Awake State and Sleep State
26-01019-005
Exterior Lighting
16,667
Table 1, Parameters
The Bulkhead Module, Chassis Module (CHM), and
instrumentation control unit (ICU) are, as a group, in
an awake state or a sleep state depending on vehicle
conditions. When any of these electronic components
are awakened, the remaining components wake up if
they are not already awake. When the BHM, CHM,
and ICU are in an awake state, the odometer reading
appears on the dash driver display screen.
One of the following actions will cause the BHM, CHM,
or ICU to go into an awake state:
• opening the door switch
• turning on the hazard switch
• turning the ignition switch to any position other
than off
• turning on the headlight/parking light switch
• depressing the service brake
The BHM, CHM, and ICU will enter a sleep state when
they are no longer actively controlling any outputs or
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050/1
54.12
Bulkhead Module
Bulkhead Module Replacement
Replacement
IMPORTANT: It is normally not necessary to replace
the Bulkhead Module (BHM). Removing and installing
the BHM should be a last resort to solving electrical
problems, unless the unit needs replacing due to
physical damage.
Follow troubleshooting procedures in this section to
solve electrical problems before replacing the Bulkhead Module. If troubleshooting indicates a malfunction of the module, try flashing the parameters and the
software before replacing the module. For flashing instructions, see Subject 110.
11. Connect the bulkhead harnesses B5 through B7
to the BHM on the cab side of the frontwall.
12. Connect the bulkhead harnesses B1 through B4
to the BHM on the engine side of the frontwall.
13. Connect the batteries.
14. Close the hood.
15. For instructions on flashing the BHM, see Subject
110.
4
Also check the external wiring. See Troubleshooting
300.
5
3
See Section 54.00, Subject 050, for information about
the M2 electrical system and Section 54.00, Troubleshooting 300, for information on troubleshooting
the entire M2 electrical system.
6
2
1. Open the hood.
7
2. Disconnect the negative leads from the batteries.
1
NOTE: The bulkhead module is located on the frontwall
slightly below and outboard of the steering column.
See Fig. 1.
3. Disconnect bulkhead harnesses B1 through B4
from the engine side of the frontwall. See Fig. 2.
4. Disconnect bulkhead harnesses B5 through B7
from the bulkhead module on the cab side of the
frontwall. See Fig. 3.
5. Remove the tread plate from the driver door entry.
6. Remove the kick panel from the left side of the
driver footwell.
7. Remove the five Torx® capscrews that secure the
BHM to the cab side of the frontwall, then remove
the BHM by pulling it through the opening into the
cab.
8
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2.
3.
4.
5.
6.
7.
8.
f543870
B1, Forward Chassis Harness
B2, Engine Harness
B3, Frontwall Harness
B4, Frontwall Harness
Frontwall
B5, Dash Harness
B6, Dash Harness
B7, Dash Harness
Fig. 1, Bulkhead Module Harness Connections
8. Place the BHM through the frontwall opening
from the cab side, then secure it with five Torx
capscrews and torque them 48 lbf1in (540 N1cm).
9. Install the kickpanel in the left side of the driver
footwell and secure it with Torx capscrews.
10. Install the tread plate at the driver door entry.
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54.12
Bulkhead Module
Bulkhead Module Replacement
2
1
1
3
3
2
4
4
5
5
09/25/2001
1.
2.
3.
4.
5.
f543915
Wiper Linkage Arm
Bulkhead Module
Hood Support Bracket
Quarter Fender
Power Distribution Module
Fig. 2, Bulkhead Module from the Engine Side
100/2
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1.
2.
3.
4.
5.
f543916
Driver Footwell Kick Panel
B5, Dash Harness
B6, Dash Harness
B7, Dash Harness
Bulkhead Module
Fig. 3, Bulkhead Module from the Cab Side
Business Class M2 Workshop Manual, Supplement 10, September 2006
Bulkhead Module
54.12
Flashing the Bulkhead Module
Flashing the Bulkhead Module
When the Bulkhead (BHM) is flashed, both the application software and reference parameters are flashed
to the BHM.
Flashing is done in ServiceLink® in the BHM "Flashing"
screen. See the ServiceLink User Guide for more
information on flashing.
Normally, it is only necessary to flash the BHM in one
of the following situations:
• When, as a last resort in the troubleshooting
process, the BHM is suspected of being faulty.
This is to confirm that the problem is hardware
related.
• When a replacement BHM is installed on a
vehicle that originally had software version 6.1.
In all other situations, it is only necessary to perform
the "Refresh Features List" in ServiceLink in the "Features" screen. This applies the appropriate reference
parameters to the BHM specific to the vehicle. See
the ServiceLink User Guide for more information on
refreshing the features list.
NOTE: Pay particular attention to the first "NOTICES"
screen when you open ServiceLink. This screen will
contain timely details on matters pertaining to successfully flashing and applying reference parameters to the
BHM.
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54.12
Bulkhead Module
Troubleshooting
IMPORTANT: The following is a general description of
how the M2 electrical system works. ServiceLink® is
the diagnostic tool for troubleshooting the M2 electrical
system. For specific circuit and pin information for how
the vehicle is wired, go to the Configuration screen in
ServiceLink and select the specific function in which
you are interested. To troubleshoot specific inputs and
outputs of this system, go to the Templates screen in
ServiceLink and select the template for the function in
which you are interested.
signal to the BHM. The BHM reacts by cycling the
compressor. The HVAC control panel contains the
logic to prevent the compressor from cycling more
than four times per minute.
The BHM monitors the A/C compressor clutch wiring
and is capable of detecting a shorted circuit when the
A/C clutch is being driven. Faults discovered by the
BHM may be reported on the J1939 and/or J1708
datalinks and may be viewed through ServiceLink.
Input and Output Conditions
Contents of Subject 300
A/C Clutch Function
Table 1 displays the A/C clutch system inputs to the
BHM and how it will react to these inputs.
Alternator Charging Function (optional)
Fault Conditions
Backup Function
Table 2 displays how the BHM handles faults that it
encounters in the A/C clutch system. The reference
parameters that program the BHM determine whether
or not a fault code is broadcast. Therefore, even if
the BHM detects a fault, a fault code may not be
transmitted. If the BHM is programmed to transmit fault
codes, they can be viewed through ServiceLink. Fault
messages may be transmitted on either or both the
J1939 and J1708 datalinks until the ignition switch is
off.
Cigar Lighter Function
Clutch Switch Function
Horn (electric) Function
Ignition System
Ignition System, Accessory Power Function
Ignition System, Ignition Power Function
Ignition System, Ignition Switch Function
3
Low Air Pressure Warning Function
Park Brake (pneumatic) Function
Wake Function
A/C Clutch Function
J1939
Description
The HVAC control panel does not directly control the
clutch on the A/C compressor. When the driver selects
the A/C button and other control conditions are met,
the control panel sends an A/C clutch request signal
to the Bulkhead Module (BHM). See Group 83 for
more information. Upon receiving this input, the BHM
responds by activating the A/C compressor clutch. See
Fig. 1.
Compressor cycling is handled in the same
manner. When the control panel determines that
the compressor needs to be cycled, it sends a
Business Class M2 Workshop Manual, Supplement 10, September 2006
BHM
2
J1708
4
5
1
f040543
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2.
3.
4.
5.
Instrumentation Control Unit
Bulkhead Module
HVAC Control Panel
Binary Pressure Switch
A/C Compressor Clutch
Fig. 1, A/C Clutch Function
300/1
54.12
Bulkhead Module
Troubleshooting
Alternator Charging Function
(optional)
until the BHM detects 14 volts at the alternator "I"
terminal. Once off, the NO CHARGE light remains
off until the BHM detects 0 volts at the alternator "I"
terminal. See Fig. 2.
Description
Input and Output Conditions
NOTE: Some vehicles will have the alternator "I"
terminal hardwired directly to the NO CHARGE light
on the ICU.
Table 3 displays the charging system inputs to the
BHM and how it will react to these inputs.
The NO CHARGE light on the Instrumentation Control
Unit (ICU) is an optional indicator used to alert
the operator to the presence of a problem with the
alternator. The Bulkhead Module (BHM) monitors a
voltage input from the "I" terminal on the alternator
and sends a J1939 message to the ICU to report
the status of the alternator. This message is used by
the ICU to turn the NO CHARGE light on or off. The
NO CHARGE light illuminates when the BHM does
not detect voltage at the "I" terminal of the alternator.
Once illuminated, the NO CHARGE light remains on
2
1
3
J1939
BHM
f040544
11/28/2001
1. Alternator
2. Bulkhead Module
3. Instrumentation Control Unit
Fig. 2, Alternator Charging Function
A/C Clutch Function Input/Output Conditions
Output from BHM
Inputs to BHM
Ignition Switch
A/C Clutch Request
A/C Clutch
On/Acc
On
Engaged
On/Acc
Off
Not Engaged
Off
On
Not Engaged
Table 1, A/C Clutch Function Input/Output Conditions
A/C Clutch Function Fault Conditions
Description of Fault
Action Taken by BHM
Status and or position of the BHM will assume the ignition switch is on.
ignition switch is in error.
A/C clutch wiring is shorted. BHM may transmit a J1939 and/or a J1708 fault message.
Table 2, A/C Clutch Function Fault Conditions
300/2
Business Class M2 Workshop Manual, Supplement 10, September 2006
54.12
Bulkhead Module
Troubleshooting
Alternator Charging Function Input/Output Conditions
Input to BHM
from Alternator
"I" Terminal
Output from BHM via J1939 Message to
ICU
Output from ICU
14 volts
Charge status of J1939 message is high.
NO CHARGE light is
off.
0 volts
Charge status of J1939 message is low.
NO CHARGE light is
on.
Table 3, Alternator Charging Function Input/Output Conditions
4
Backup Function
Description
The backup function provides a warning to anyone
standing behind when the vehicle begins to back up.
When the transmission is placed into reverse gear, the
Bulkhead Module (BHM) sends a J1939 message to
the Chassis Module (CHM) activating the backup lights
and alarm.
The BHM is capable of detecting short circuits in
the backup lights/alarm wiring on the CHM. Faults
discovered by the BHM may be reported on the J1939
and/or J1708 datalinks and may be viewed through
ServiceLink.
Input and Output Conditions
Activation of the backup lights/alarm is different depending on the transmission type. A manual transmission uses a standard switch to tell the BHM when
the transmission is in reverse. Automatic transmissions
send a J1939 message to the BHM when they are
placed into reverse gear. See Fig. 3 and Fig. 4. Also
see Table 4.
Business Class M2 Workshop Manual, Supplement 10, September 2006
5
6
J1939
CHM
BHM
ON
ACC
OFF
2
J1708
J1939
7
3
1
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6.
7.
f040556
Instrumentation Control Unit
Bulkhead Module
Ignition Switch
Reverse Switch
Chassis Module
Backup Lights
Optional Backup Alarm
Fig. 3, Backup Function, Manual Transmission
300/3
54.12
Bulkhead Module
Troubleshooting
Table 5 displays the backup lights and alarm system
inputs to the BHM and how it will react to these inputs.
Trans
ECU
4
5
J1939
6
J1939
CHM
BHM
ON
ACC
OFF
2
J1708
J1939
7
3
1
f040549a
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6.
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Instrumentation Control Unit
Bulkhead Module
Ignition Switch
Transmission ECU
Chassis Module
Backup Lights
Optional Backup Alarm
Fig. 4, Backup Function, Automatic Transmission
Backup Function
Transmission Type
Manual transmission
Input to BHM
Backup switch is closed.
BHM Conclusion
Transmission is in reverse.
J1939 message from transmission
indicates either:
Automatic transmissions
• Current Gear = Reverse
Transmission is in reverse.
• Selected Gear = Reverse
• Gear Range = R
Table 4, Backup Function
Backup Function Input/Output Conditions
Inputs to BHM
Output from BHM
Ignition
Switch
Transmission
Status
Backup Lights/Alarm*
On/Acc
Reverse
On
On/Acc
Not Reverse
Off
Off
Reverse
Off
Off
Not Reverse
Off
* Via J1939 message to the CHM
Table 5, Backup Function Input/Output Conditions
300/4
Fault Conditions
Table 6 displays how the BHM handles faults it encounters in the backup lights and alarm system. The
reference parameters that program the BHM determine whether or not a fault code is broadcast. Therefore, even if the BHM detects a fault, a fault code
may not be transmitted. If the BHM is programmed to
transmit fault codes, they can be viewed through ServiceLink. Fault messages may be transmitted on either
or both the J1939 and J1708 datalinks until the ignition
switch is turned off.
Business Class M2 Workshop Manual, Supplement 10, September 2006
54.12
Bulkhead Module
Troubleshooting
On vehicles with automatic transmissions, the BHM
has the following additional J1939 fault messages.
Any J1939 fault message may be transmitted until the
ignition switch is turned off. See Table 7.
Cigar Lighter Function
Description
The cigar lighter provides 12 volt power (up to 15
amps) to any device plugged into it. The Bulkhead
Module (BHM) supplies power at this port regardless
of the position of the ignition switch.
Fault Conditions
Table 8 displays how the BHM handles faults that it
encounters in the cigar lighter system. The reference
parameters that program the BHM determine whether
or not a fault code is broadcast. Therefore, even if
the BHM detects a fault, a fault code may not be
transmitted. If the BHM is programmed to transmit fault
codes, they can be viewed through ServiceLink. Fault
messages may be transmitted on either or both the
J1939 and J1708 datalinks until the ignition switch is
turned off.
1
2
3
The BHM is capable of detecting short circuits in the
cigar lighter wiring. Faults discovered by the BHM may
be reported on the J1939 and/or J1708 datalinks and
may be viewed through ServiceLink. See Fig. 5.
J1939
BHM
J1708
f040546
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1. Instrumentation Control Unit
2. Bulkhead Module
3. Cigar Lighter
Fig. 5, Cigar Lighter Function
Backup Function Fault Conditions
Description of Fault
Action Taken by BHM
Ignition switch status is in error.
BHM will assume the ignition switch is in the on position and may transmit a fault
message on the J1939 and/or J1708 datalinks.
Backup lights/alarm wiring shorted.
BHM may transmit a J1939 and/or a J1708 fault message.
Table 6, Backup Function Fault Conditions
Backup Function Fault Conditions, Automatic Transmissions
Description of Fault
Action Taken by BHM
BHM fails to receive five consecutive J1939 messages from
the transmission ECU.
BHM may transmit a J1939 fault message and assume the
transmission is in reverse.
Transmission ECU sends an error indicator in the J1939
message to the BHM.
BHM may transmit a J1939 fault message and assume the
transmission is in reverse.
Table 7, Backup Function Fault Conditions, Automatic Transmissions
Cigar Lighter Function Fault Conditions
Description of Fault
Action Taken by BHM
Cigar lighter wiring shorted. BHM may transmit a J1939 and/or a J1708 fault message.
Table 8, Cigar Lighter Function Fault Conditions
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54.12
Bulkhead Module
Troubleshooting
Clutch Switch Function
Input and Output Conditions
Description
Table 9 displays the clutch switch system inputs to the
BHM and how it will react to these inputs.
NOTE: Only vehicles with a manual or three-pedal automated mechanical (AMT) transmission are equipped
with a clutch pedal. The clutch switch is integrated into
the clutch pedal assembly. See Section 54.25 for information on the starter control system including the
bottom-of-clutch switch input.
The Bulkhead Module (BHM) reads the position of the
top-of-clutch and bottom-of-clutch switches. The topof-clutch switch information is broadcast over J1939
datalink for use by the engine and, optionally, other
ECUs. The bottom-of-clutch switch input is used for a
starter system interlock; the switch position information
is not broadcast for other ECUs. The BHM, engine
ECU, and transmission ECU use the clutch position
status information as inputs for systems such as
starting and cruise control.
While both switches are mounted to the clutch pedal
assembly, they are activated at different times during
the operation of the clutch. As the clutch pedal is
pressed towards the floor, the top-of-clutch switch
changes from closed to open, and the BHM transmits
this information over the J1939 datalink. Based on this
information, if the cruise control is active the engine
ECU will turn it off. As the clutch pedal reaches the
floor, the bottom-of-clutch switch is activated. It will
change from open to closed, as the pedal is fully
depressed.
The BHM monitors the top- and bottom-of-clutch
switch wiring and is capable of detecting error
conditions. Faults discovered by the BHM will be
reported on the J1939 and/or J1708 datalinks and
may be viewed through ServiceLink. See Fig. 6.
Fault Conditions
Table 10 displays how the BHM handles faults it
encounters in the clutch switch system. The reference
parameters that program the BHM determine whether
or not a fault code is broadcast. Therefore, even if
the BHM detects a fault, a fault code may not be
transmitted. If the BHM is programmed to transmit fault
codes, they can be viewed through ServiceLink. Fault
messages may be transmitted on either or both the
J1939 and J1708 datalinks until the ignition switch is
turned off.
Trans
ECU
5
4
3
6
J1939
J1939
BHM
J1708
2
J1939
1
Engine
ECU
f040547
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2.
3.
4.
5.
6.
Engine ECU
Bottom-of-Clutch Switch (normally open)
Top-of-Clutch Switch (normally closed)
Bulkhead Module
Transmission ECU
Instrumentation Control Unit
Fig. 6, Clutch Switch Function
Clutch Function Input/Output Conditions
Inputs to BHM
300/6
Output from BHM
Top-of-Clutch Switch
Bottom-of-Clutch Switch
Closed
Open
Open
Closed
J1939 Clutch Switch Message
Clutch pedal is released.
Clutch pedal is depressed.
Business Class M2 Workshop Manual, Supplement 10, September 2006
54.12
Bulkhead Module
Troubleshooting
Clutch Function Input/Output Conditions
Inputs to BHM
Output from BHM
Top-of-Clutch Switch
Bottom-of-Clutch Switch
Open
Open
Closed
Closed
J1939 Clutch Switch Message
Clutch pedal is partially
depressed.
Clutch pedal is released.*
* This is an error condition, see the Fault Conditions paragraph for more information.
Table 9, Clutch Function Input/Output Conditions
Clutch Function Fault Conditions
Inputs to BHM
Top of Clutch
Switch
Bottom of Clutch
Switch
Closed
Closed
Output from BHM
BHM transmits a J1939 and/or a J1708 fault
message.
Table 10, Clutch Function Fault Conditions
Horn (electric) Function
messages may be transmitted on either or both the
J1939 and J1708 datalinks until the horn switch is off.
Description
The Bulkhead Module (BHM) controls the horn. A
single horn is standard; dual horns are optional. There
is no change in functionality between single and dual
horns. When the driver activates the horn switch, the
circuit is completed and grounds the signal line to the
BHM. The BHM activates the horn circuit as long as
the signal line is grounded. The BHM is capable of
detecting short conditions. Faults discovered by the
BHM may be reported on the J1939 and/or J1708
datalinks and may be viewed through ServiceLink. See
Fig. 12.
Horn (electric) Function Input/Output Conditions
Horn Switch
Electric Horn
Pressed
Activate (noise)
Released
Deactivate (silent)
Table 11, Horn (electric) Function Input/Output
Conditions
4
3
BHM
Input and Output Conditions
2
Table 11 indicates how the horn should react based
on the inputs from the signal line.
J1939
5
Fault Conditions
Table 12 displays how the BHM will handle faults that it
encounters in the electric horn system. The reference
parameters that program the BHM determine whether
or not a fault code is broadcast. Therefore, even if
the BHM detects a fault, a fault code may not be
transmitted. If the BHM is programmed to transmit fault
codes, they can be viewed through ServiceLink. Fault
J1708
1
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f040550
Instrumentation Control Unit
Bulkhead Module
Horn Switch
Horn
Dual Horns (optional)
Fig. 7, Horn (electric) Function
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54.12
Bulkhead Module
Troubleshooting
Horn (electric) Function Fault Conditions
Description of Fault
Action Taken by BHM
Horn output shorted.
BHM may transmit a J1939 and/or
a J1708 fault message.
Table 12, Horn (electric) Function Fault Conditions
datalinks and may be viewed through ServiceLink. See
Fig. 8.
Input and Output Conditions
Table 13 displays the accessory power system inputs
to the BHM and how it reacts to these inputs.
Fault Conditions
Ignition System
Description
The ignition system is made up of multiple
components. The Bulkhead Module (BHM) takes
input from the ignition switch and uses the information
to crank the starter and to supply ignition and
accessory power to the vehicle. See Fig. 8.
Ignition System, Accessory Power
Function
Description
The Bulkhead Module (BHM) continuously monitors
the position of the ignition switch to determine if
the accessory power outputs should be energized.
Accessory power is provided to the HVAC control panel
and the radio. Separate power feeds are used for each
of the accessory outputs.
The BHM is capable of detecting shorted circuits in
the accessory power outputs. Faults discovered by
the BHM will be reported on the J1939 and/or J1708
4
3
Table 14 displays how the BHM will handle faults it
encounters in the accessory power system. The reference parameters that program the BHM determine
whether or not a fault code is broadcast. Therefore,
even if the BHM detects a fault, a fault code may not
be transmitted. If the BHM is programmed to transmit
fault codes, they can be viewed through ServiceLink.
Fault messages may be transmitted on either or both
the J1939 and J1708 datalinks until the ignition switch
is turned off.
Ignition System, Ignition Power
Function
Description
The Bulkhead Module (BHM) continuously monitors
the position of the ignition switch to determine if the
ignition power outputs should be energized. Ignition
power is provided to the following components:
• antilock brake system electronic control unit
(ABS ECU)
• instrumentation control unit (ICU)
• engine ECU
• transmission ECU
J1939
• vehicle control unit (VCU), if equipped
BHM
ON
STR ACC
J1708
Separate power feeds are used for each of the ignition
outputs.
OFF
2
1
5
Accessory Power (12V+)
Ignition Switch
Bulkhead Module
Instrumentation Control Unit
Ignition Power (12V+)
01/15/2002
1.
2.
3.
4.
5.
Fig. 8, Ignition System Function
300/8
f040554
The BHM is capable of detecting shorted circuits in the
ignition power outputs. Faults discovered by the BHM
may be reported on the J1939 and/or J1708 datalinks
and may be viewed through ServiceLink. See Fig. 8.
Input and Output Conditions
Table 15 displays the ignition power system inputs to
the BHM and how it will react to these inputs.
Business Class M2 Workshop Manual, Supplement 10, September 2006
54.12
Bulkhead Module
Troubleshooting
Fault Conditions
Input and Output Conditions
Table 16 displays how the BHM handles faults it
encounters in the ignition power system. The reference
parameters that program the BHM determine whether
or not a fault code is broadcast. Therefore, even if
the BHM detects a fault, a fault code may not be
transmitted. If the BHM is programmed to transmit fault
codes, they can be viewed through ServiceLink. Fault
messages may be transmitted on either or both the
J1939 and J1708 datalinks until the ignition switch is
turned off.
Table 17 displays how the BHM reacts given the status
of the ignition switch.
Ignition System, Ignition Switch
Function
Fault Conditions
Table 18 displays ignition switch circuit conditions
that will create a fault. The reference parameters that
program the BHM determine whether or not a fault
code is broadcast. Therefore, even if the BHM detects
a fault, a fault code may not be transmitted. If the
BHM is programmed to transmit fault codes, they can
be viewed through ServiceLink. Fault messages may
be transmitted on either or both the J1939 and J1708
datalinks until a valid ignition switch status is detected.
Accessory Power Function Input/Output Conditions
Description
The ignition switch has four positions: off, accessory,
on, and start. The Bulkhead Module (BHM) continuously monitors the position of the ignition switch and
broadcasts this information on the J1939 datalink.
There are three circuits that run from the ignition switch
to the BHM. One is for the accessory position, one is
for the on position, and one is for the start position.
The BHM monitors the ignition switch wiring and is
capable of detecting error conditions in the ignition
switch circuits. Faults discovered by the BHM may be
reported on the J1939 and/or J1708 datalinks and may
be viewed through ServiceLink. See Fig. 8.
Input to the BHM
from the Ignition
Switch
Output from the BHM to the
Accessory Power Circuits
Acc
On
Off
Off
On
On
Start
Off
Table 13, Accessory Power Function Input/Output
Conditions
Accessory Power Function Fault Conditions
Description of Fault
Action Taken by BHM
Ignition switch is in error.
BHM will assume the ignition switch is on, and will transmit a fault message
on the J1939 and/or J1708 datalinks.
The accessory power output wiring is
shorted.
BHM may transmit a J1939 and/or a J1708 fault message.
Table 14, Accessory Power Function Fault Conditions
Ignition Power Function Input/Output Conditions
Input to the BHM from the Output from the BHM to
Ignition Switch
the Ignition Power Circuits
Acc
Off
Off
Off
On
On
Start
On
Table 15, Ignition Power Function Input/Output
Conditions
Business Class M2 Workshop Manual, Supplement 10, September 2006
300/9
54.12
Bulkhead Module
Troubleshooting
Ignition Power Function Fault Conditions
Description of Fault
Action Taken by BHM
BHM will assume the ignition switch is on, and may transmit a fault message
on the J1939 and/or J1708 datalinks.
Ignition switch is in error.
The ignition power output wiring is shorted. BHM may transmit a J1939 and/or a J1708 fault message.
Table 16, Ignition Power Function Fault Conditions
Ignition Switch Function Input/Output Conditions
Inputs to BHM
Output from BHM
Ignition Switch Accessory
Circuit
Ignition Switch On Circuit
Ignition Switch Start Circuit
J1939 Ignition Switch
Position Message
Open
Open
Open
Off
Closed
Open
Open
Acc
Closed
Closed
Open
On
Open
Closed
Closed
Start
Open
Open
Closed
On*
Closed
Open
Closed
On*
Open
Closed
Open
On*
* These are error conditions. For more information see the "Fault Conditions" paragraph under the "Ignition System, Ignition Switch Function" heading.
Table 17, Ignition Switch Function Input/Output Conditions
Ignition Switch Function Fault Conditions
Description of Fault
Action Taken by BHM
Ignition Switch
Accessory Circuit
Ignition Switch On
Circuit
Ignition Switch
Start Circuit
Open
Open
Closed
BHM transmits a J1939 and/or a J1708 fault message.
Closed
Open
Closed
BHM transmits a J1939 and/or a J1708 fault message.
Open
Closed
Open
BHM transmits a J1939 and/or a J1708 fault message.
Table 18, Ignition Switch Function Fault Conditions
Low Air Pressure Warning Function
Description
The Chassis Module (CHM) monitors the low air
pressure switches from the air management unit
(AMU) and sends a J1939 message to the Bulkhead
Module (BHM) indicating the switch status. The BHM
sends a J1939 message to the instrumentation control
unit (ICU) indicating whether the low air pressure
warning light should be on or off. The ICU alerts
the driver when the air pressure in the primary or
secondary air systems is below 65 to 75 psi (450 to
300/10
520 kPa) by illuminating a telltale indicator. There are
two normally open pressure switches wired in series
in the AMU pressure switch module. Both switches
must close in order to complete the circuit to the CHM
to change the low air pressure warning status from on
to off. See Fig. 9. Faults discovered by the BHM may
be reported on the J1939 and/or J1708 datalinks and
may be viewed through ServiceLink.
Business Class M2 Workshop Manual, Supplement 10, September 2006
54.12
Bulkhead Module
Troubleshooting
Input and Output Conditions
5
3
Table 19 displays the low air pressure warning inputs
to the BHM and how it will react to these inputs.
6
4
J1939
CHM
S
BHM
Fault Conditions
J1939
P
Table 20 displays how the BHM handles faults that it
encounters in the low air pressure warning system.
The reference parameters that program the BHM
determine whether or not a fault code is broadcast.
Therefore, even if the BHM detects a fault, a fault code
may not be transmitted. If the BHM is programmed
to transmit fault codes, they can be viewed through
ServiceLink. Fault messages may be transmitted on
either or both the J1939 and J1708 datalinks.
AMU
2
J1708
7
1
f040555
01/15/2002
1.
2.
3.
4.
5.
6.
7.
NOTE: This fault also occurs when the CHM is unable
to determine the switch status. This does not necessarily mean that the low air pressure switches are faulty.
Air Management Unit (AMU)
Primary Air
Secondary Air
Low Air Pressure Switches
Chassis Module
Bulkhead Module
Instrumentation Control Unit
Fig. 9, Low Air Pressure Warning Function
Low Air Pressure Warning Function Input/Output Conditions
Input to BHM from
CHM
Output from BHM to
ICU
Input from ICU to
BHM
Primary Air Pressure
Switch
J1939 Low Air
Pressure Switch
Status Message
J1939 Low Air
Pressure Warning
Light Command
Message
J1939 Low Air
Pressure Warning
Light Status Message
Open
Open
Open
Enabled
On
Open
Closed
Open
Enabled
On
Closed
Open
Open
Enabled
On
Closed
Closed
Closed
Disabled
Off
Inputs to CHM
Secondary Air
Pressure Switch
Table 19, Low Air Pressure Warning Function Input/Output Conditions
Low Air Pressure Warning Function Fault Conditions*
Description of Fault
CHM transmits J1939 low air pressure status unavailable or
in error to the BHM.
Action Taken by BHM
BHM may transmit J1939 low air pressure warning light
status unavailable.
* This fault also occurs when the CHM is unable to determine the switch status. This does not necessarily mean that the low air pressure switches are faulty.
Table 20, Low Air Pressure Warning Function Fault Conditions
Business Class M2 Workshop Manual, Supplement 10, September 2006
300/11
54.12
Bulkhead Module
Troubleshooting
Park Brake (pneumatic) Function
Description
The Chassis Module (CHM) monitors the park brake
switch in the air management unit (AMU) and sends
a J1939 message to the Bulkhead Module (BHM).
The BHM sends the park brake status via a J1939
message to the instrumentation control unit (ICU). The
park brake status is also broadcast over the J1939
datalink for other ECUs to use. The ICU alerts the
operator when the parking brake is engaged. When
the park brake is not set and the driver’s door is open,
the ICU will chime. See Fig. 10. Faults discovered by
the BHM may be reported on the J1939 and/or J1708
datalinks and may be viewed through ServiceLink.
the BHM detects a fault, a fault code may not be
transmitted. If the BHM is programmed to transmit fault
codes, they can be viewed through ServiceLink. Fault
messages may be transmitted on the J1939 and/or
J1708 datalinks.
NOTE: This fault also occurs when the CHM is unable
to determine the switch status. This does not necessarily mean that the park brake pressure switch is faulty.
2
3
4
J1939
J1939
CHM
J1939
AMU
Input and Output Conditions
5
BHM
J1708
6
Table 21 displays the park brake system inputs to the
BHM and how it will react to these inputs.
Fault Conditions
Table 22 displays how the BHM handles faults that it
encounters in the park brake system. The reference
parameters that program the BHM determine whether
or not a fault code is broadcast. Therefore, even if
1
f040558
01/15/2002
1.
2.
3.
4.
5.
6.
Air Management Unit (AMU)
Park Brake Pressure Switch
Chassis Module
Bulkhead Module
Park Brake Status
Instrumentation Control Unit
Fig. 10, Park Brake (pneumatic) Function
Park Brake (pneumatic) Function
Input to CHM from Park
Brake Pressure Switch
Input to BHM from CHM
via J1939 Park Brake
Status
Output from BHM to ICU
via J1939 Park Brake
Light Status
Closed
Engaged
On
Open
Disengaged
Off
Table 21, Park Brake (pneumatic) Function
Park Brake (pneumatic) Function Fault Conditions*
Description of Fault
Action Taken by BHM
CHM transmits J1939 park brake switch status unavailable or BHM may transmit J1939 message park brake light status
in error to the BHM.
unavailable.
* This fault also occurs when the CHM is unable to determine the switch status. This does not necessarily mean that the park brake pressure switch is faulty.
Table 22, Park Brake (pneumatic) Function Fault Conditions
Wake Function
See Subject 050 for general information on the awake
state and sleep state of the Bulkhead Module (BHM).
300/12
Business Class M2 Workshop Manual, Supplement 10, September 2006
Bulkhead Module
54.12
Troubleshooting
Wake-up Initiation
The Bulkhead Module (BHM) wakes up the Chassis
Module (CHM), Expansion Module (EXM), and Switch
Expansion Module (SEM) by pulling the wake circuits
from 12V down to approximately 4V. The EXM and
SEM are optional.
The wake circuits remain active at 4V only as long as
one or more of the inputs that initiate a wake remain
active. See Fig. 11 for wake circuit connectivity and
inputs that initiate a wake.
The BHM wakes up the instrumentation control unit
(ICU) by applying 12V to its wake circuit.
The BHM initiates other modules to wake up when one
or more of the following inputs to the BHM is active:
• driver door open
• passenger door open (optional input)
• headlight switch on
• hazard lights switch on
• ignition switch on
The CHM initiates a wake to the BHM, which in turn
wakes all other modules when the:
• service brakes are applied.
When any of the above initiating inputs are inactive, the
wake circuits float back to approximately 12V (except
the wake circuit between the BHM and ICU). The ICU
wake circuit remains active at 12V until the system
goes to sleep.
Sleep Initiation
When the inputs that initiate a wake are active for
60 seconds, the BHM signals the modules to go to
sleep by sending a message via J1939. The BHM also
causes the ICU to go to sleep by removing power from
its wake circuit.
Business Class M2 Workshop Manual, Supplement 10, September 2006
300/13
54.12
Bulkhead Module
Troubleshooting
Hazard lights switch = on
Headlight switch = on
Ignition = on
Driver door = open
Passenger door = open
One or more inputs must
be active to wake the BHM
and other modules.
B6.A2
B4.H
B5.D
B1.B
BHM
81C
14F
ICU
C1.2
C4.A
C4.A
C2.D16
14E
CHM
EXM
SEM
Service brake
switch = on
06/26/2006
Inputs that cause the
CHM to wake the BHM
and other modules.
f544874
Fig. 11, Simplified Wake Schematic
Troubleshooting Quick Checks
If the ICU chimes when the door is opened, check for
an open or short to power in the wake circuit between
the BHM and CHM—the BHM cannot determine the
park brake status and assumes it is not set while the
door is open.
300/14
If the ICU does not display the odometer when the
door is opened, check fuse 20 and check for an open
in the BHM to ICU wake circuit.
To thoroughly check wake functionality, follow the
troubleshooting procedures in Table 23.
Business Class M2 Workshop Manual, Supplement 10, September 2006
54.12
Bulkhead Module
Troubleshooting
Wake Circuits Troubleshooting Procedures
Test
No.
1
Test Procedure
Open the "Wake Function" Datalink Monitor template. See
Fig. 12.
Test Result
Yes
Check the inputs that are remaining
active.
For example, if the driver door switch
remains active (open) when the door
is closed, check the door switch itself
and the circuit wiring.
Put the system into a sleep state by:
• Closing the doors.
• Turning off the headlight switch.
Repair as necessary.
• Turning off the hazard lights switch.
Go to test no. 2.
• Turning off the ignition switch.
• Removing your foot from the brake pedal.
Action
No
Are any of the BHM and CHM initiating inputs still in an active
state on the template (yellow)?
2
If everything works correctly after meeting the conditions in
test no. 1, the system should go to sleep within 60 seconds.
The template indicates this when all of the annunciators show
an exclamation mark (!)*.
If the system is not working correctly, one or more of the Wake
Circuits in the right column of the "Wake Function" Datalink
Monitor template remains active (yellow) after 60 seconds.
Yes
Go to test no. 6.
Go to test no. 3.
No
Within 60 seconds of meeting the conditions in test no. 1, do
all of the annunciators on the template show an exclamation
mark (!)*?
3
In the second column of the template under "Other Module
Wake Circuits–Status" is the status of all the annunciators
"LOW-Wake" (yellow)?
NOTE: Disregard the annunciators for modules not on the
vehicle; these will show an exclamation mark (!)*.
Check the wake circuits between the
BHM and the following modules for a
short to ground:
Yes
• CHM
• EXM
• SEM
Repair as necessary.
4
If the B5.D BHM to ICU annunciator status is "ON" in the
second column of the template under "BHM Wake
Circuits–Status," continue with this test. If not, go to test no. 5.
No
Go to test no. 4.
Yes
The wake circuit between the BHM
and ICU is shorted to power.
Repair as necessary.
Disconnect BHM connector B5.
Test for voltage on pin B5.D (harness side).
Go to test no. 5.
No
Is voltage present?
Business Class M2 Workshop Manual, Supplement 10, September 2006
300/15
54.12
Bulkhead Module
Troubleshooting
Wake Circuits Troubleshooting Procedures
Test
No.
5
Test Procedure
Test Result
In the second column of the template under "BHM Wake
Circuits–Status," check the status of the annunciator labeled
Yes
If this is the only active annunciator,
replace the BHM.
No
Check the multiplexed modules for
ignition circuits that are shorted to
power (not powering down when the
ignition is off). If no problem is found,
the system may not be going to sleep
because the BHM is not sending the
J1939 go-to-sleep message. Try a test
BHM to confirm.
Yes
Go to test no. 8.
B1.B BHM to CHM
B4.H BHM to EXM
B6.A2 BHM to SEM.
Is the annunciator status "LOW-Wake" (yellow)?
6
Starting with the system in the sleep state, activate one of the
inputs that initiates a wake, such as opening the driver’s door.
Action
Go to test no. 7.
If the system is functioning properly, all of the annunciators on
the template in the second column should be active (yellow)
for ECUs equipped on the vehicle as long as the input remains
active. For example, the door is open.
No
NOTE: If the vehicle is not equipped with an SEM or EXM, it is
normal for the status of these annunciators to be "!"*.
Are all of the appropriate second column annunciators active?
7
Which annunciator is not active?
B5.D BHM to Replace the BHM.
ICU
B1.B BHM to Replace the BHM.
CHM
B4.H BHM to
EXM
B6.A2 BHM
to SEM
Any one of
the "Other
Module
Wake
Circuits–
Status" for
ECUs that
are on the
vehicle.
300/16
Check for an open in the wake circuit
between the BHM and the module
that is not showing active.
If OK, check power, ground, and the
J1939 datalink to the ECU that is not
responding.
Business Class M2 Workshop Manual, Supplement 10, September 2006
54.12
Bulkhead Module
Troubleshooting
Wake Circuits Troubleshooting Procedures
Test
No.
8
Test Procedure
Test Result
Does the ICU wake up when the door is opened? This is
indicated by the odometer being displayed.
Yes
Action
No problem found.
Check the wake circuit between the
BHM and ICU for open.
If OK, check fuse 20 and VBAT2
power supply to BHM B4.G.
No
If OK, ICU may be faulty.
Repair as necessary.
* The exclamation mark (!) will show on the versions of this template released with ServiceLink version 4.0 and higher. On templates released in ServiceLink
versions prior to 4.0, if the annunciator is flashing, the flashing takes precedence over the status that it is displaying.
Table 23, Wake Circuits Troubleshooting Procedures
M2 − Wake Function
APPLIES TO:
M2
TEMPLATE VER. 1.0, 6/13/06
BHM inputs that initiate
a wake:
BHM wake circuits−
status:
B6.A7 Driver’s Door
Switch
B5.D BHM to ICU
Status
OFF
OPEN
B6.A6 Passenger
Door Switch
Status
B1.B BHM to CHM
B4.H BHM to EXM
B6.A2 BHM to SEM
Status
ON
B6.B8 Hazard
Switch Status
B6.A3 Ignition
Switch
Status
Other module wake
circuits − status:
C4.A CHM
Status
ON
HIGH
Status
Status
C4.A EXM
HIGH
ON
BHM inputs that initiate
a wake:
C3.G Service Brake
Switch
Status
HIGH
OPEN
Headlamp Switch
Status
Status
Status
J1.2 SEM
Status
HIGH
RELEASED
I
View
J1939
Codes
ENTER TEST MODE
EXIT TEST MODE
OFF
Wake−up Initiation:
These are the following input conditions that will cause the entire M2 MUX system (BHM, CHM,
ICU, EXM, and SEM) to wake up:
(1) One or more of these BHM input conditions are met: Driver door = open; Passenger door =
open; Headlamp switch = on; Hazard switch = on; or Ignition switch = on
−OR−
(2) The following CHM input condition is met: Service brakes = applied
All of the wake circuits (except the ICU) will be in "LOW−wake" mode as long as one of the wake
inputs is active (e.g. as long as the driver’s door is open, all of the module wake circuits will be
"LOW−awake" state. When no inputs that initiate a wake are active, all the wake circuit (except
the ICU) will be in the "HIGH" state.
The BHM wakes the ICU by applying a constant 12V to it’s wake circuit input. The status of the
BHM to ICU wake circuit will remain on until the BHM determines it is time for everything to go to
sleep.
Sleep Initiation:
When all the wake input conditions are inactive for 60 seconds, the BHM will send a J1939
message to all the modules (except ICU) to go into sleep mode. The BHM commands the ICU to
go to sleep by removing power from its wake circuit. When everything is in sleep mode, J1939
communication will stop and all the annunciators will show "I" until a wake is initated by
activating one of the wake initiating inputs (e.g. opening the driver’s side door).
Testing:
Go to sleep test: Close the doors, turn off the headlights and hazard lights, turn the ignition off,
and keep your foot off the brake pedal. All of the inputs that initiate a wake should be inactive. If
not check those circuits. After 60 seconds of inactive inputs, all of the modules should go to
sleep.
Wake test: Starting with everything asleep, activate one of the inputs that initiates a wake (e.g.
open the driver’s side door). As long as the input is active, all the wake circuits should be "LOW−
Wake" and the ICU wake circuit should be ON. Deactive the input, then verify the wake circuits
go to "HIGH" (except the ICU, which will remain ON until the BHM commands all the modules to
go to sleep). If a wake circuit does not change to "LOW−Wake" when one of the wake initiating
inputs is active, then that wake circuit is probably open. If all the wake circuits show low when all
the wake initiating inputs are inactive, this indicates there is a short to ground in one of the wake−
up lines between the BHM and one of the MUX modules.
NOTE: Not all vehicles are equipped with and EXM or SEM. Disregard annunciators for modules
not on the vehicle.
06/23/2006
f060188
Fig. 12, Wake Function Datalink Monitor Template
Business Class M2 Workshop Manual, Supplement 10, September 2006
300/17
54.12
Bulkhead Module
Specifications
See Fig. 2 for maximum allowable current load for the
full BHM output pins (part numbers A06-40959-000
and A06-40959-002).
20A
B5.F − Cigar Lighter Output
12A
B3.E − Horn
12A
Combined
See Fig. 3 for an illustration of the BHM with pinout
assignments and harness connections.
4
5
3
6
2
12A
B5.H − Panel Lamps
B7.A1 − Panel Lamps (Smart Switch)
12A
Combined
B4.F − SPARE (Left Heated Mirror)
B4.E − SPARE (Right Heated Mirror)
6.7A
Combined
B6.A9 − Accessory (HVAC)
B6.A10 − Accessory (Radio)
6.7A
Combined
B5.A − Battery (Dome Lamps)
B7.A12 − Battery (Smart Switch)
6.7A
Combined
B6.A8 − Ignition (VCU)
B2.K − Ignition (Engine)
B1.P − Ignition (ABS)
B2.L − Ignition (Trans)
B1.F − Fuel Water Sensor Power
6.7A
6.7A
6.7A
6.7A
8
09/26/2001
1.
2.
3.
4.
5.
6.
7.
8.
f543870
B1, Forward Chassis Harness
B2, Engine Harness
B3, Frontwall Harness
B4, Frontwall Harness
Frontwall
B5, Dash Harness
B6, Dash Harness
B7, Dash Harness
Fig. 1, Bulkhead Module Harness Connections
Business Class M2 Workshop Manual, Supplement 10, September 2006
B5.G − SPARE (Ignition)
12A
Combined
7
1
B5.E − SPARE (Utility Light/Spotlight)
B4.M − SPARE (Utility Light/Spotlight)
6.7A
Combined
6.7A
6.7A
6.7A
6.7A
6.7A
11/24/2004
Bulkhead Module
See Fig. 1 for an illustration of the Bulkhead Module
(BHM) Harness Connections.
B5.D − Wake Up (Instrument Cluster)
B5.B − Dome Lamps Switched
B1.L − Left High Beam
B1.R − Left Low Beam
B5.C − Clearance Lamps
B1.K − Tail/License Plate/Trailer Relay
B3.F − Wiper High
B3.H − Wiper Low
B3.G − Washer Pump
B2.M − AC Clutch
B4.B − Starter Relay (Crank)
See Note A below.
f544533
NOTE A: Pulse Width Modulated Output
Fig. 2, Maximum Allowable Current Load for the
Full-Feature Bulkhead Module Output Pins (part
numbers A06-40959-000 and A06-40959-002)
400/1
54.12
Bulkhead Module
Specifications
4
A B C D E F
G H J K L M
A B C D
H G F E
A B C D
E F G H
A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12
03/31/2004
B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 B11 B12
S R P N M L K J
H G F E D C B A
A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12
1
B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 B11 B12
2
A B C D E F G
H J K L M N P
3
5
6
7
f543868
NOTE: Pins shown are viewed toward the BHM or wire insertion end of the harness connector.
1.
2.
3.
4.
B1,
B2,
B3,
B4,
5. B5, Dash Harness
6. B6, Dash Harness
7. B7, Dash Harness
Forward Chassis Harness
Engine Harness
Frontwall Harness
Frontwall Harness
Fig. 3, Bulkhead Module With Pinout Assignments and Harness Connections
Connector B1 Forward Chassis Harness Pinouts
Connector Pin
Signal Name
B1-A
—
—
B1-B
Module Wake-Up Signal
Digital Input/
Output
B1-C
Spare Digital Input 4
Digital Input
B1-D
400/2
Signal Type
—
—
B1-E
Ground
Power Ground
B1-F
Fuel/Water Sensor Ignition Power
Digital Output
B1-G
Ground
Signal Ground
B1-H
J1587+ Datalink
Datalink
Business Class M2 Workshop Manual, Supplement 10, September 2006
54.12
Bulkhead Module
Specifications
Connector B1 Forward Chassis Harness Pinouts
Connector Pin
Signal Name
Signal Type
B1-J
Battery Power (VBAT5)
Power
B1-K
Tail Lamps/License Plate Lamp/Trailer Tail Relay
Digital Output
B1-L
Left High Beam
Digital Output
B1-M
Fuel/Water Separator (spare digital input 5)
Digital Input
B1-N
Battery Power (VBAT3)
Power
B1-P
ABS Ignition Power
Digital Output
B1-R
Left Low Beam
Digital Output
B1-S
J1587– Datalink
Datalink
Table 1, Connector B1 Forward Chassis Harness Pinouts
Connector B2 Engine Harness Pinouts
Connector Pin
Signal Name
Signal Type
B2-A
J1587+ Datalink
Datalink
B2-B
J1939+ Datalink
Datalink
B2-C
J1587+ Datalink
Datalink
B2-D
J1587– Datalink
Datalink
B2-E
—
B2-F
—
—
—
B2-G
Backup Switch (spare digital input 3)
Digital Input
B2-H
J1587– Datalink
Datalink
B2-J
J1939– Datalink
Datalink
B2-K
Engine ECU Ignition Power
Digital Output
B2-L
Transmission ECU Ignition Power
Digital Output
B2-M
A/C Clutch
Digital Output
B2-N
B2-P
—
—
Alternator Charging
Digital Input
Table 2, Connector B2 Engine Harness Pinouts
Connector B3 Frontwall Harness Pinouts
Connector Pin
Signal Name
Signal Type
B3-A
J1939– Datalink
Datalink
B3-B
J1939+ Datalink
Datalink
B3-C
Wiper Parked Position
Digital Input
B3-D
Main Battery Power (VBAT1)
Power
B3-E
Horn
Digital Output
B3-F
Wiper Motor High Speed
Digital Output
Business Class M2 Workshop Manual, Supplement 10, September 2006
400/3
54.12
Bulkhead Module
Specifications
Connector B3 Frontwall Harness Pinouts
Connector Pin
Signal Name
Signal Type
B3-G
Washer Pump
Digital Output
B3-H
Wiper Motor Low Speed
Digital Output
Table 3, Connector B3 Frontwall Harness Pinouts
Connector B4 Frontwall Harness Pinouts
Signal Name
Connector Pin
Signal Type
B4-A
Air Filter Restriction/Spare #9
Digital Input
B4-B
Starter Relay
Digital Output
B4-C
Ground
Ground
B4-D
Spare Digital Input 2
Digital Input
B4-E
Right Heated Mirror (spare digital output)
Digital Output
B4-F
Left Heated Mirror (spare digital output)
Digital Output
B4-G
Main Battery Power (VBAT2)
Power
B4-H
Module Wake-Up Signal
Digital Input/Output
B4-J
—
—
B4-K
Main Battery Power (VBAT4)
Power
B4-L
Washer Fluid Level (spare digital input 8)
Digital Input
B4-M
Utility Light/Spotlight (spare digital output)
Digital Output
Table 4, Connector B4 Frontwall Harness Pinouts
Connector B5 Dash Harness Pinouts
Connector Pin
Signal Name
Signal Type
B5-A
Dome Lamps Battery
Digital Output
B5-B
Dome Lamps Switched
Digital Output
B5-C
Clearance Lamps (cab)
Digital Output
B5-D
Instrument Cluster Wake-Up
Digital Output
B5-E
Utility Light/Spotlight (spare digital output)
Digital Output
B5-F
Cigar Lighter
Digital Output
B5-G
Ignition Power, Other (spare digital output)
Digital Output
B5-H
Panel Lamps
Digital Output
Table 5, Connector B5 Dash Harness Pinouts
Connector B6 Dash Harness Pinouts
Connector Pin
400/4
Signal Name
Signal Type
B6-A1
Ignition Switch Accessory Position
Digital Input
B6-A2
Module Wake-Up Signal
Digital Input
Business Class M2 Workshop Manual, Supplement 10, September 2006
54.12
Bulkhead Module
Specifications
Connector B6 Dash Harness Pinouts
Connector Pin
B6-A3
Signal Name
Signal Type
Ignition Switch On
B6-A4
Digital Input
—
—
B6-A5
Ignition Switch Start
Digital Input
B6-A6
Passenger Door Open (spare digital input 10)
Digital Input
B6-A7
Driver Door Open
Digital Input
B6-A8
VCU Ignition Power
Digital Output
B6-A9
HVAC Power
Digital Output
B6-A10
Radio Power
Digital Output
B6-A11
J1587– Datalink
Datalink
B6-A12
J1587+ Datalink
Datalink
B6-B1
Horn Switch
Digital Input
B6-B2
Top of Clutch Switch (spare digital input 7)
Digital Input
B6-B3
Bottom of Clutch Switch (spare digital input 6)
Digital Input
B6-B4
—
—
B6-B5
Panel Lamps Increase
Digital Input
B6-B6
Panel Lamps Decrease
Digital Input
B6-B7
A/C Clutch Request
Digital Input
B6-B8
Hazard Switch
Digital Input
B6-B9
Headlamp Switch PARK Position
Digital Input
B6-B10
Headlamp Switch On Position
Digital Input
B6-B11
Headlamp Switch On 2 Position
Digital Input
B6-B12
—
—
Table 6, Connector B6 Dash Harness Pinouts
Connector B7 Dash Harness Pinouts
Connector Pin
Signal Name
Signal Type
B7-A1
Panel Lamps (smart switch)
Digital Output
B7-A2
Smart Switch 3 ID 1
Analog Input
B7-A3
Smart Switch 3 ID 2
Analog Input
B7-A4
Smart Switch 3 Input
Analog Input
B7-A5
Smart Switch 3 Indicator
Digital Output
B7-A6
Smart Switch 4 ID 1
Analog Input
B7-A7
Smart Switch 4 ID 2
Analog Input
B7-A8
Smart Switch 4 Input
Analog Input
B7-A9
Smart Switch 4 Indicator
Digital Output
B7-A10
Smart Switch 5 ID 1
Analog Input
Business Class M2 Workshop Manual, Supplement 10, September 2006
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54.12
Bulkhead Module
Specifications
Connector B7 Dash Harness Pinouts
Connector Pin
Signal Name
Signal Type
B7-A11
Smart Switch 5 ID 2
Analog Input
B7-A12
Smart Switch Battery Power
Digital Output
B7-B1
Smart Switch 1 ID 1
Analog Input
B7-B2
Smart Switch 1 ID 2
Analog Input
B7-B3
Smart Switch 1 Input
Analog Input
B7-B4
Smart Switch 1 Indicator
Digital Output
B7-B5
Smart Switch 2 ID 1
Analog Input
B7-B6
Smart Switch 2 ID 2
Analog Input
B7-B7
Smart Switch 2 Input
Analog Input
B7-B8
Smart Switch 2 Indicator
Digital Output
B7-B9
Ground
Signal Ground
B7-B10
Smart Switch 5 Indicator
Digital Output
B7-B11
Smart Switch 5 Input
Analog Input
B7-B12
—
—
Table 7, Connector B7 Dash Harness Pinouts
Power Supply Fuses and Associated Outputs for the Bulkhead Module
BHM Power Input
BHM Power
Input Pin
Fuse Supplying BHM
Power Input
BHM Outputs Supplied
Power Out
Power In
VBAT1
400/6
B3.D
BHM Output Pin
Fuse 22 (30A)
Battery (dome lamps)
B5.A
Battery (smart switches)
B7.A12
Ignition (VCU)
B6.A8
Ignition (engine)
B2.K
Ignition (ABS)
B1.P
Ignition (trans)
B2.L
Fuel Water Sensor Power
B1.F
Dome Lamps Switched
B5.B
Left Low Beam
B1.R
A/C Clutch
B2.M
Smart Switch 1 Indicator
B7.B4
Smart Switch 2 Indicator
B7.B8
Smart Switch 3 Indicator
B7.A5
Smart Switch 4 Indicator
B7.A9
Smart Switch 5 Indicator
B7.B10
Battery (smart switch)
B7.A12
Business Class M2 Workshop Manual, Supplement 10, September 2006
54.12
Bulkhead Module
Specifications
Power Supply Fuses and Associated Outputs for the Bulkhead Module
BHM Power Input
BHM Power
Input Pin
Fuse Supplying BHM
Power Input
BHM Outputs Supplied
Power Out
Power In
VBAT2
VBAT3
VBAT4
VBAT5
B4.G
B1.N
B4.K
B1.J
BHM Output Pin
Fuse 20 (30A)
Fuse 18 (30A)
Fuse 15 (30A)
Fuse 7 (30A)
Accessory (HVAC)
B6.A9
Accessory (radio)
B6.A10
Wake Up (instrument cluster)
B5.D
Left High Beam
B1.L
Wiper High
B3.F
Horn
B3.E
Wiper Low
B3.H
Spare 8.0A HSD (ignition)
B5.G
Panel Lamps
B5.H
Panel Lamps (smart switch)
B7.A1
Clearance Lamps
B5.C
Tail Lamps/License Plate Lamp/Trailer Tail
Relay
B1.K*
Washer Pump
B3.G
12V Output (cigar lighter)
B5.F
Spare 8.5A (utility light/spotlight)
B5.E / B4.M
Left Heated Mirror
B4.F
Right Heated Mirror
B4.E
* This output supplies power to the Chassis Module pass-through for the tail lamps, license plate lamp, and trailer tail lamp relay.
Table 8, Power Supply Fuses and Associated Outputs for the Bulkhead Module
NOTE: Currents listed are the maximum allowable
combined current load for each output pin or group
of pins. When maximum allowable current load is
exceeded, the BHM software will shut off the output
pin or group of pins.
In Test Mode, the outputs will deliver more current load
than the maximum allowable current values shown.
When testing, do not exceed the maximum combined
values for more than a few minutes or the life of the
output driver inside the BHM may be shortened.
Business Class M2 Workshop Manual, Supplement 10, September 2006
400/7
54.12
Bulkhead Module
Bulkhead Module Fault Code Information
General Information
Subject 410 contains information on all proprietary
Bulkhead Module (BHM) fault codes for J1587 and
J1939 datalink protocols, how to view these codes,
and what the codes mean. Each fault code contains
three distinct pieces of information.
J1587 fault codes consist of the following elements in
the order listed:
• Module Identifier (MID) – Identifies which electronic control unit (ECU) the fault is coming from.
The J1587 MID identifying all Bulkhead Module
information faults is 164.
• Subsystem Identifier (SID) – Indicates what
function on the ECU has failed. All J1587 SIDs
for the BHM are listed in Table 1.
• Failure Mode Indicator (FMI) – Indicates in what
way the function failed.
J1939 fault codes consist of the following elements in
the order listed:
• Suspect Parameter Number (SPN) – Indicates
what function on the ECU has failed. All J1939
SPNs for the BHM are listed in Table 2.
• Failure Mode Indicator (FMI) – Indicates in what
way the function failed.
See Table 3 for a list of all failure mode identifiers for
both datalink protocols.
References such as BHM B1.A indicate that the fault
is sensed to be coming from the Bulkhead Module,
connector B1, pin A. Similarly, CHM indicates the
Chassis Module on a vehicle.
J1587 fault codes are shown under J1708 in ServiceLink. J1587 and J1708 are essentially the same
datalink protocol.
As the SAE J1939 subcommittee approves new SPNs
for use in J1939 messaging on a continual basis,
J1939 SPNs used for diagnostic messages could
change when the Bulkhead Module part changes.
These changes could impact any diagnostic message
with an SPN value of 6915 or higher.
• Source Address (SA) – Identifies which ECU the
fault is coming from. The J1939 SA identifying all
Bulkhead Module faults is 33.
J1587 SIDs for Bulkhead Module (BHM) MID 164
SID
Description
Possible FMI
000
Backlighting Dimmer Switch Fault
7
001
Clutch Switch Fault
7
002
Reserved for Future Use
–
003
Headlamp Switch Disagreement–Both park and on inputs are closed.
7
004
Multifunction Turn Signal Switch High Beam Input Fault
2
005
Ignition Switch Fault
7
006
Marker Interrupt Switch Fault
7
007
Multifunction Turn Signal Switch Disagreement–Both wiper high and wiper low inputs are
on.
2
008
Multifunction Turn Signal Switch Disagreement–Wiper on/off is off and wiper high or low
input is on.
2
009
Wiper Park Input Fault
7
010
ICU3-M2 Hazard Switch CAN Feedback Error
2
011
Multifunction Turn Signal Switch Left Turn Signal Input Fault
2
012
Multifunction Turn Signal Switch Right Turn Signal Input Fault
2
013
Multifunction Turn Signal Switch Washer Switch Input Fault
2
014
Multifunction Turn Signal Switch Wiper On/Off Input Fault
2
Business Class M2 Workshop Manual, Supplement 10, September 2006
410/1
54.12
Bulkhead Module
Bulkhead Module Fault Code Information
J1587 SIDs for Bulkhead Module (BHM) MID 164
SID
Multifunction Turn Signal Switch Wiper Low Input Fault
2
016
Multifunction Turn Signal Switch Wiper High Input Fault
2
017
Wheel-Based Vehicle Speed CAN Message Error
2
018
Wake-up Hardware Fault–Modules are kept awake.
7
019
Unknown Keep Awake Fault–Modules are kept awake.
7
020
Extra Smart Switch
7
021
Duplicate Smart Switch
7
022
Missing Smart Switch
7
023
Fifth Wheel Solenoid Unexpected Pressure Feedback
7
024
Fifth Wheel Solenoid No Pressure Feedback
7
025
End of Frame Air Unexpected Pressure Feedback
7
026
End of Frame Air No Pressure Feedback
7
027
Axle Lift Unexpected Pressure Feedback
7
028
Axle Lift No Pressure Feedback
7
029
Suspension Dump Unexpected Pressure Feedback
7
030
Suspension Dump No Pressure Feedback
7
031
Suspension Proportioning Unexpected Pressure Feedback
7
032
Suspension Proportioning No Pressure Feedback
7
033
Cigar Lighter Output Fault
7
034
BHM/ICU3-M2 Ignition Mismatch
7
035
BHM/ICU3-M2 Hazard Switch Mismatch
2
036
BHM/ICU3-M2 Wiper Park Mismatch
2
037
Missing Transmission CAN Message
9
038
Missing Chassis Module CAN Message
9
Reserved for Future Use
–
039–049
410/2
Possible FMI
Description
015
050
BHM B1.A
3, 4
051
BHM B1.F, B1.P, B2.K, B2.L, B6.A8
5, 6
052
BHM B1.J
3, 4
053
BHM B1.K, B5.C
5, 6
054
BHM B1.L
5, 6
055
BHM B1.N
3, 4
056
BHM B1.R
5, 6
057
BHM B2.M
5, 6
058
BHM B3.D
3, 4
059
BHM B3.E
3, 4, 5, 6
060
BHM B3.F
5, 6
Business Class M2 Workshop Manual, Supplement 10, September 2006
54.12
Bulkhead Module
Bulkhead Module Fault Code Information
J1587 SIDs for Bulkhead Module (BHM) MID 164
SID
Description
Possible FMI
061
BHM B3.G
5, 6
062
BHM B3.H
5, 6
063
BHM B4.B
064
BHM B4.E, B4.F
065
BHM B4.G
3, 4
066
BHM B4.K
3, 4
067
BHM B4.M, B5.E
068
BHM B5.A, B7.A12
5, 6
069
BHM B6.A9, B6.A10
5, 6
070
BHM B5.B
5, 6
071
BHM B5.D
5, 6
072
BHM B5.F
3, 4, 5, 6
073
BHM B5.G
3, 4, 5, 6
074
BHM B5.H, B7.A1
3, 4, 5, 6
075
CHM C1.A, C1.H, C1.J
5, 6
076
CHM C1.G, C2.H, C3.N
5, 6
077
CHM C1.L
5, 6
078
CHM C1.N
5, 6
079
CHM C1.P, C2.E, C3.R
5, 6
080
CHM C2.A
3, 4
081
CHM C2.F, C4.C, C4.D, C4.L, C4.M
3, 4, 5, 6
082
CHM C3.A
3, 4, 5, 6
083
CHM C3.C, C3.D
5, 6
084
CHM C3.E
3, 4
085
CHM C3.F
3, 4
086
CHM C3.J
3, 4
087
CHM C3.K
5, 6
088
CHM C3.L
5, 6
089
CHM C4.F
5, 6
090
CHM C4.J
3, 4
091
CHM C4.K
5, 6
092
CHM C4.P
3, 4
093
CHM C5.A
3, 4
094
CHM C5.B
3, 4
095
CHM C5.F
3, 4
096
CHM C5.G
3, 4
Business Class M2 Workshop Manual, Supplement 10, September 2006
5, 6
3, 4, 5, 6
3, 4, 5, 6
410/3
54.12
Bulkhead Module
Bulkhead Module Fault Code Information
J1587 SIDs for Bulkhead Module (BHM) MID 164
SID
Possible FMI
Description
097
CHM C5.H
3, 4
098
CHM C5.J
3, 4
099
CHM C5.L
3, 4
100
CHM C5.M
3, 4
101
EXM
3, 4, 5, 6
Table 1, J1587 SIDs for Bulkhead Module (BHM) MID 164
J1939 SPNs for Bulkhead Module (BHM) SA 33
SPN
Description
Possible FMI
70
Parking Brake Switch
80
Washer Fluid Level
2
84
Wheel-based Vehicle Speed
19
96
Fuel Level
19
97
Water In Fuel Indicator
19
163
Transmission Current Range
177
Transmission Oil Temperature Sensor
523
Transmission Current Gear
12, 19
524
Transmission Selected Gear
12, 19
597
ABS Service Brake Switch
2
598
Clutch Switch
7
879
Front Left Turn Signals Output Fault
880
Trailer Stop Lamp Relay Output Fault
4
881
Front Right Turn Signals Output Fault
5, 6
882
Park/Marker Lights Output Fault
973
Engine Retarder Selection
1487
Backlighting Dimmer Switch Fault
1550
A/C Clutch Output Fault
2003
Missing Transmission CAN Message
9
2071
Missing Chassis Module CAN Message
9
6915
Lamp and Gauge Ignition Output Fault
4, 5, 6
6916
BHM/ICU3-M2 Wiper Park CAN Message Mismatch
2
6917
BHM/ICU3-M2 Hazard Switch CAN Message Mismatch
2
6918
Missing Smart Switch
7
6919
Duplicate Smart Switch
7
6920
Extra Smart Switch
7
6921
Unknown Keep Awake Fault–Modules are kept awake.
7
410/4
2
12, 19
3, 4
5, 6
4, 5, 6
19
7
5, 6
Business Class M2 Workshop Manual, Supplement 10, September 2006
54.12
Bulkhead Module
Bulkhead Module Fault Code Information
J1939 SPNs for Bulkhead Module (BHM) SA 33
SPN
Description
6922
Wake-up Hardware Fault–Modules are kept awake.
7
6923
Wiper Parked Input Fault
7
6924
Multifunction Turn Signal Switch Disagreement–Wiper on/off input is off and wiper high or
low input is on.
2
6925
Multifunction Turn Signal Switch Disagreement–Both wiper high and wiper low inputs are
on.
2
6926
Marker Interrupt Switch Fault
6927
Utility Lamp Output Fault
6928
Suspension Proportioning No AMU Pressure Feedback
7
6929
Suspension Proportioning Unexpected AMU Pressure Feedback
7
6930
Suspension Proportioning Solenoid Output Fault
3, 4, 5, 6
6931
Suspension Dump No AMU Pressure Feedback
7
6932
Suspension Dump Unexpected AMU Pressure Feedback
7
6933
Suspension Dump Solenoid Output Fault
3, 4, 5, 6
6934
Spotlights Output Fault
3, 4, 5, 6
6935
Snow Plow Relay Output Fault
3, 4, 5, 6
6936
Rear 2 Differential Lock AMU Pressure Feedback Fault
6937
Rear 2 Differential Lock Solenoid Output Fault
6938
Rear 1 Differential Lock AMU Pressure Feedback Fault
6939
Rear 1 Differential Lock Solenoid Output Fault
3, 4, 5, 6
6940
Optional Feature Output Fault
3, 4, 5, 6
6941
Heated Mirrors Output Fault
3, 4, 5, 6
6942
Interaxle AMU Pressure Feedback Fault
6943
Interaxle Solenoid Output Fault
6944
Fuel Water Separator Heater Output Fault
6945
Front Differential Lock AMU Pressure Feedback Fault
6946
Front Differential Lock Solenoid Output Fault
6947
Fog Lamp Output Fault
6949
Fire Pump AMU Pressure Feedback Fault
6950
Fire Pump Solenoid Output Fault
6951
Fifth Wheel Slide No AMU Pressure Feedback
7
6952
Fifth Wheel Slide Unexpected AMU Pressure Feedback
7
6953
Fifth Wheel Slide Solenoid Output Fault
6954
End of Frame Air No AMU Pressure Feedback
7
6955
End of Frame Air Unexpected AMU Pressure Feedback
7
6956
End of Frame Air Solenoid Output Fault
6957
Daytime Running Lights (DRL) Output Fault
Business Class M2 Workshop Manual, Supplement 10, September 2006
Possible FMI
7
3, 4, 5, 6
7
3, 4, 5, 6
7
7
3, 4, 5, 6
4, 5, 6
7
3, 4, 5, 6
5, 6
7
3, 4, 5, 6
3, 4, 5, 6
3, 4, 5, 6
5, 6
410/5
54.12
Bulkhead Module
Bulkhead Module Fault Code Information
J1939 SPNs for Bulkhead Module (BHM) SA 33
SPN
Description
Possible FMI
6958
Brake Line Air Dryer Output Fault
6959
Axle Shift AMU Pressure Feedback Fault
6960
Axle Shift Solenoid Output Fault
6961
Axle Lift No AMU Pressure Feedback
7
6962
Axle Lift Unexpected AMU Pressure Feedback
7
6963
Axle Lift Solenoid Output Fault
3, 4, 5, 6
6964
Air Horn Solenoid Output Fault
5, 6
6965
BHM VBAT 5 Input Fault
3, 4
6966
BHM VBAT 4 Input Fault
3, 4
6967
BHM VBAT 3 Input Fault
3, 4
6968
BHM VBAT 2 Input Fault
3, 4
6969
BHM VBAT 1 Input Fault
3, 4
6970
Wiper High Output Fault
5, 6
6971
Wiper Low Output Fault
5, 6
6972
Multifunction Turn Signal Switch Wiper High Input Fault
2
6973
Multifunction Turn Signal Switch Wiper Low Input Fault
2
6974
Multifunction Turn Signal Switch Wiper On/Off Input Fault
2
6975
ICU3-M2 Wiper Park CAN Feedback Error
6976
Washer Pump Output Fault
6977
Multifunction Turn Signal Switch Washer Switch Input Fault
2
6978
Multifunction Turn Signal Switch Right Turn Signal Input Fault
2
6979
Multifunction Turn Signal Switch Left Turn Signal Input Fault
6980
Right Stop Lamp Output Fault
5, 6
6981
Left Stop Lamp Output Fault
5, 6
6982
Wake Up Hardware Fault
5, 6
6983
Starter Relay (mag switch) Output Fault
5, 6
6984
Ignition System, Accessory Power Outputs Fault
5, 6
6985
Ignition System, Ignition Power Outputs Fault
6986
Ignition Switch Fault
6987
Taillights, Clearance Lights, License Plate Lights Output Fault
5, 6
6988
Left Low Beam Output Fault
5, 6
6989
Right Low Beam Output Fault
5, 6
6990
Left High Beam Output Fault
5, 6
6991
Right High Beam Output Fault
5, 6
6992
Multifunction Turn Signal Switch High Beam Input Fault
2
6993
Headlamp Switch Disagreement–Both park and on inputs are closed.
7
410/6
3, 4, 5, 6
7
3, 4, 5, 6
2
5, 6
2
2, 5, 6
7
Business Class M2 Workshop Manual, Supplement 10, September 2006
54.12
Bulkhead Module
Bulkhead Module Fault Code Information
J1939 SPNs for Bulkhead Module (BHM) SA 33
SPN
Description
Possible FMI
6994
ICU3-M2 Hazard Switch CAN Feedback Error
19
6995
Horn Output Fault
6996
Dome Lamps Switched Power Output Fault
6997
Cigar Lighter Output Fault
6998
Dome Lamps Battery Power Output Fault
5, 6
6999
Backup Lamps/Alarm Output Fault
5, 6
7000
Panel Lamp Backlighting PWM Output Fault
3, 4, 5, 6
5, 6
3, 4, 5, 6
3, 4, 5, 6
Table 2, J1939 SPNs for Bulkhead Module (BHM) SA 33
Failure Mode Identifiers
FMI
J1939 Description
J1587 Description
00
Data valid but above normal operational range–Most severe
level
Data valid but above normal operational range
(engine overheating)
01
Data valid but below normal operational range–Most severe
level
Data valid but below normal operational range
(engine oil pressure too low)
02
Data erratic, intermittent, or incorrect
Data erratic, intermittent, or incorrect
03
Voltage above normal or shorted high
Voltage above normal or shorted high
04
Voltage below normal or shorted low
Voltage below normal or shorted low
05
Current below normal or open circuit
Current below normal or open circuit
06
Current above normal or grounded circuit
Current above normal or grounded circuit
07
Mechanical system not responding or out of adjustment
Mechanical system not responding properly
08
Abnormal frequency, pulse width, or period
Abnormal frequency, pulse width, or period
09
Abnormal update rate
Abnormal update rate
10
Abnormal rate of change
Abnormal rate of change
11
Root cause not known
Failure mode not identifiable
12
Bad intelligent device or component
Bad intelligent device or component
13
Out of Calibration
Out of Calibration
14
Special Instructions
Special Instructions
15
Data valid but above normal operational range–Least severe
level
Reserved for future assignment by the SAE
Subcommittee
16
Data valid but above normal operational range–Moderately
severe level
–
17
Data valid but below normal operational range–Least severe
level
–
18
Data valid but below normal operational range–Moderately
severe level
–
19
Received network data in error
–
Table 3, Failure Mode Identifiers
Business Class M2 Workshop Manual, Supplement 10, September 2006
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