CHAPTER
13
Body Control Modules
Instructor Name: (Your Name)
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Learning Objectives
• Explain the concept of virtual fusing
• List the type of inputs and outputs used by a
typical body control module
• Discuss the reasons that most electronic
control modules used in modern trucks make
use of a reference ground
• Discuss the difference between a
conventional switch and diagnosable switch
• Describe how a body control module can act
as a turn signal flasher
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Learning Objectives (continued)
• Retrieve DTC’s stored in memory related
to the body controller
• List the main components of the
International Diamond Logic® and
Freightliner® Smart Plex™ multiplexed
electrical systems
• Describe how a Freightliner Smart Switch
operates
• Explain the concept of ghost voltage and
describe how it can lead to confusion
when diagnosing an electrical problem
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International Multiplexed
Electrical System
• Referred to as the Diamond Logic
electrical system
• Between 2001-2006 body control modules
were referred to as electrical system
controller (ESC)
• In 2007 the name was changed to the
body controller
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International ESC
Figure 13-1 International electrical system controller (ESC).
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International Body Controller
Figure 13-2
International
body controller.
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Overview of Body Controller
Figure 13-3 Overview of body controller.
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Tech Tip
Think of the J1939 data link as both being
an input and an output device for most
electronic devices. The messages
received by a module are inputs; the
messages sent by a module are the
outputs.
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Typical Body Control Module
Horn Circuit
Figure 13-5 Typical body control module horn circuit.
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Body Controller Outputs
• The body controller has three main
types of outputs:
– High side drivers
– Low side drivers
– Messages transmitted on the J1939 data link
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High Side Driver
• Capable of sourcing high levels of current
• The high side drivers used in body
controllers are power MOSFETs (FETs)
• Some FETs are capable of sourcing 20A
continuously
• Smart FETs can monitor the amount of
current that the FET is conduction
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Current Feedback For Virtual Fusing
Figure 13-6 The high side driver measures the current being
conducted and feeds back this information to the microprocessor
as a proportional voltage.
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Low Side Drivers
•
•
•
•
Current ratings of 1A or less
Commonly used in body controllers
Low side drivers sink a path to ground
Typically used to energize relay coils or
small solenoids
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Body Controller Inputs
• There are three main types of inputs
to the body controller:
– Hardwired inputs from switches and sensors
– Messages received from a proprietary switch
data link
– Messages received from the J1939 data link
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Hardwired Inputs
• Conventional switch to control electrical
devices
• Reference ground is a single ground that
all sensors and switches share
• Reference ground is connected to chassis
ground but in one location usually inside
the electronic module
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Common Reference Ground
Located in Body Controller
Figure 13-7 The common reference ground point inside of body controller is
connected to chassis ground at only one location.
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CAUTION
It is vital that any electronic system that uses
a reference ground only be grounded in
accordance with OEM recommendations.
Even though reference ground may appear to
be the same as chassis ground, connecting
the reference ground to chassis ground
outside the electronic module may result in
the truck having intermittent EMI induced
problems that are nearly impossible to
duplicate or troubleshoot.
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Open and Closed Switches
with Digital Input
Figure 13-8 Open
switch (upper) and
closed switch
(lower) with digital
input.
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Open Circuit Prevents Digital Input
From Detecting Switch is Closed
Figure 13-9 Open circuit prevents digital input from detecting that switch is closed;
input voltage should be 0V with switch closed, but is actually +12V.
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Diagnosable Switch With Contacts
Open and Closed
Figure 13-10 Diagnosable switch with contacts open and closed.
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Diagnosable Switch Open;
8V at the Input Terminal
Figure 13-11 Diagnosable switch open; 8V at input terminal.
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Diagnosable Switch Closed; 6V at
the Input Terminal
Figure 13-12 Diagnosable switch closed; 6V at input terminal.
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Diagnosable Switch Open Circuit;
12V at the Input Terminal
Figure 13-13 Diagnosable switch open circuit; 12V at input terminal.
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Switch Packs
• International trucks with body controllers
use switch packs using J1708/J1578
specification data link
• This proprietary link is not the same as the
J1708/J1587 data link connected to the
power train or ECM modules
• Switch packs are rockers that require
switch actuators installed in them
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Switch Pack with
Switch Actuators Removed
Figure 13-14 Switch pack with the switch actuators removed.
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Tech Tip
Think of high side drivers as being like
conventional relays. A small signal
provided by the microprocessor is used to
control a large amount of current.
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Body Controller Headlight Circuit
Figure 13-15 Body controller headlamp circuit. EGC contains
headlamp switch.
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Turn-Signal System, International
Truck With Body Controller
Figure 13-16 Turn-signal system on International trucks with body controller. Two
switches are inputs; four high side drivers are outputs.
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Tech Tip
The body controller only powers the
applicable trailer light relay control circuit.
The body controller does not directly
supply the current to the trailer lighting. A
conventional CPD such as a fuse or a
circuit breaker in the PDC is used to
protect the trailer wiring, not virtual fusing.
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A/C System Inputs; Outputs Is A/C
Clutch High Side Driver
Figure 13-17 Air conditioning system inputs; output is A/C clutch high side driver.
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Cruise Control Related Inputs Output
is J1939 Message to Engine ECM
Figure 13-18 Cruise control related inputs; output is J1939 message to engine ECM.
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Primary and Secondary Air
Pressure Measurement System
Figure 13-19 Primary
and secondary air
pressure measurement
system.
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Windshield Wiper System Outputs
Figure 13-20 Windshield wiper system outputs; one high side driver and two low side drivers.
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Wiper Switch Inputs and Truth Table
Figure 13-21
Wiper switch
inputs and truth
table.
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Tech Tip
An open windshield wiper switch connection
on an International truck with a body
controller causes the wiper to operate at high
speeds at any time the key switch is in the
ignition position. Additionally, a short to
ground of the windshield washer pump
control circuit will cause the windshield
wipers to operate at low speed any time the
key switch is in the ignition position because
the controller is falsely detecting that the
washer switch is depressed.
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Freightliner Multiplexed Electrical System
• Freightliner refers to their multiplexed
electrical system as SmartPlex™
• The bulkhead module (BHM) acts as the
primary command module for body and
chassis electrical systems.
• The chassis module (CHM) is the other
standard electronic module
• The CHM is a slave or dependent that
receives commands from the BHM
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Freightliner SmartPlexTM Electronic
Module Locations
Figure 13-22 Freightliner SmartPlexTM electronic module
locations.
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Bulkhead Module (BHM)
• Main electronic controller for Freightliner
SmartPlexTM electrical system
• The BHM is connected to the J1939 data link
and transmits and receives information from
other electronic modules
• The BHM is hardwired to several inputs in the
cab
• Direct hardwired high side outputs include
horn, dome light, left side low-beam and high
beam headlights
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Freightliner Smart Switch Schematic
Figure 13-25
Freightliner smart
switch schematic.
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Chassis Module (CHM)
• Contains several high side driver FETs
that source current to several chassis
electrical features
• The CHM is dependent on commands
from the BHM via the J1939 data link
• High side driver outputs include park and
marker lights, back-up lamps, turn signal
lamps, right side high and low beam
headlights and fog lamps
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Freightliner Multifunction Switch
Figure 13-28 Freightliner
multifunction switch.
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Freightliner Multiplexed
Headlamp Control
Figure 13-29 Freightliner multiplexed headlamp control.
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Troubleshooting The Multiplexed Truck
• Best if performed with OEM diagnostic
software and a PC, referred to as a electronic
service tool (EST)
• Software for Freightliner trucks is
ServiceLink®
• Software for International trucks is diamond
Logic®
• This software permits viewing diagnostic
trouble codes by the body controller and
EGC, along with fault descriptions
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International Diagnostic
Code Retrieval
• Place the ignition switch in the ignition or
accessory position
• Set the park brake
• Depress the cruise control ON and
RESUME switches at the same time
• The EGC will indicate the number of DTCs
that exist
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Diagnostic Trouble Codes Display
Figure 13-32 Diagnostic trouble codes as displayed in instrument
panel cluster odometer display.
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SAE J1939 Suspect
Parameter Number
Figure 13-33 SAE J1939 suspect parameter number (SPN).
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SAE J1939 Failure Mode Indicator
Figure 13-34 SAE J1939 failure mode indicator.
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ORH Condition at a Pulled-Up Input
With Open Circuit
Figure 13-36 ORH condition at a pulled-up input with an open circuit.
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ORL Condition at a Pulled-Up Input
with Grounded Circuit
Figure 13-37 ORL condition at a pulled-up input with a ground circuit.
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ORL Condition at a Pulled-Down
Input With Open Circuit
Figure 13-38 ORL condition at a pulled-down input with an open circuit.
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Summary
• The body control module on International
High Performance Vehicles is called the
electrical system controller (ESC) on
model year 2001-2006 trucks and the
body controller on 2007 and later year
trucks. The body controller or ESC
contains a microprocessor. The body
controller or ESC uses information
obtained from input sources to control the
outputs.
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Summary(continued)
• Outputs of the body controller include high side
drivers, low side drivers, and messages on the
J1939 data link.
• Input sources for the body controller include
messages from the J1939 data link, messages
from the switch link, and hardwired inputs such as
switches and sensors.
• A reference ground scheme is commonly used in
automotive electronics to minimize the effects of
electromagnetic interference and to improve
measurement accuracy for sensor circuits.
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Summary(continued)
• A diagnosable switch is a special switch
that provides specific values of resistance,
unlike a conventional switch, which is
either an open circuit or a near 0Ω. A
diagnosable switch is connected to an
analog input. This permits circuit failures
such as an open circuit or a shorted-toground circuit to be diagnosed.
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Summary(continued)
• The body controller controls several electrical
system features, including headlamps, turn
signals, stop lamps, and windshield wipers.
The various switches act as inputs to the
body controller through either hardwiring or
multiplexing. The body controller
microprocessor makes decisions based on its
programming and provides an output in the
form of energizing a high side driver,
energizing low side driver, or transmitting a
data link message.
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Summary(continued)
• Self-diagnostics assists in troubleshooting the
body controller. Diagnostic trouble codes may
be logged to indicate a circuit that is out of
range high or out of range low.
• The Freightliner SmartPlexTM system uses
two or more separate modules to control
body electrical features. The bulkhead
module (BHM) controls the chassis module
(CHM) via the J1939 data link.
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Summary(continued)
• The Freightliner SmartPlexTM uses optional
smart switches to control electrical system
features. Each smart switch contains two
identification resistors that uniquely define the
switch function.
• The instrument cluster in the Freightliner
SmartPlexTM system is called the ICU. The
ICU acts as the input device for the stalk
mounted multifunction switch. The ICU
transmits the status of the multifunction
switch inputs on the J1939 data link.
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Summary(continued)
• Diagnostic trouble codes (DTCs) are used
to indicate that an electrical module has
detected and abnormal condition. DTCs
may indicate a sensor in-range operating
condition, such as engine coolant
temperature is too high. DTCs may also
indicate sensor out of range conditions,
such as open circuits or shorts to grounds.
A J1939 DTC consists of an SPN and FMI.
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Summary(continued)
• Ghost voltage describes an open circuit
measurement of a voltage by a DMM in a
circuit with high resistance. Ghost voltage
can result in misdiagnosis.
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