CHAPTER
15
Modern Truck
Electrical Systems
Instructor Name: (Your Name)
Copyright © 2014 Delmar, Cengage Learning
Learning Objectives
• Explain the basic functionality of an
electronically controlled automatic
transmission
• Discuss the functionality of an automated
manual transmission
• Define the terms PRNDL, NSBU, VIM, chuff
test, differential braking, and ABS modulator
• Explain how an air ABS system and traction
control operate
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Learning Objectives (continued)
• Test an ABS wheel sensor circuit
• Describe how a fault detected by a trailer
ABS ECU causes the trailer ABS warning
lamp to illuminate in the truck instrument
panel
• Discuss the operation of an Eaton electric
hybrid system
• Discuss the difference between a series
hybrid and parallel hybrid truck
• List the steps to troubleshoot a wiring
problem with the J1939 data link
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Allison World Transmission
• Currently the most common in North America
• Full authority control; transmission will only
shift when commanded by the transmission
ECU
• WTEC – World Transmission Electronic
Controls
• Electronic shift control; no hard line to the
transmission
• Transmission ECU can use information from
the J1708/1587 & J1939 data link
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World Transmission Controls
Figure 15-2 World
transmission components.
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Allison WT Electronic Shift Selectors
Figure 15-3 Allison WT electronic shift selectors.
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Allison World Transmission
(continued)
• WT Transmissions uses 3 reluctance type
speed sensors: engine, turbine, and tail
shaft
• There are two types of solenoids used:
normally open and normally closed
• Allison Diagnostic Optimized Connection
(DOCTM) troubleshooting software
• WT Generation 4 can display diagnostic
trouble codes on digital display
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WT Speed Sensors
Figure 15-4
WT speed
sensors.
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WT Solenoids
Figure 15-6 WT normally closed solenoid. Figure 15-7 WT normally open solenoid.
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WT Hydraulic Schematic –
Third Range Setting
Figure 15-9 WT hydraulic schematic – third range attained.
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Automated Manual Transmissions
• AMT – Automated manual transmission
• Manual transmission with automatic
control
• One or two pedal system
• Eaton Fuller is currently the most common
• Driver interface and transmission ECU
communicate via private J1939 network
called the EPL
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Eaton Driver Interface
Figure 15-11 Eaton driver interface.
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Automated Manual Transmissions
(continued)
• Primary inputs to ECU are from three
transmission mounted speed sensors and
rail select and gear select position sensors
• Eaton AutoShift – Three pedal system
• Eaton UltraShift – Two pedal system
• Eaton ServiceRanger™ is a PC-based
EST used to diagnose an Eaton AMT
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Eaton AMT Speed Sensors
Figure 15-12 Eaton AMT speed sensors.
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Gear and Rail Select Position Sensors
Figure 15-13 Gear and rail select position sensors.
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Antilock Brake System
• Reluctance-type speed sensors on both front
and at least two rear wheels on a tandem
axle tractor
• Typical ABS tone wheel has 100 teeth
• The ABS ECU measures the frequency of the
waveform produced
• ABS modulators control air flow to service
brake chambers to prevent brake lock up
• Modulators are designed to revert to nonABS in the event of failure
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ABS Schematic For Straight Truck
Figure 15-15 ABS schematic for straight truck.
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Four Channel ABS With ATC
Figure 15-18 Four-channel ABS with ATC.
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ABS Modulator with
Integral Relay Valve
Figure 15-19 Air ABS brake modulator with integral relay valve.
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Antilock Brake System (continued)
• A chuff test is a brief actuation of the
modulation coil at start up
• A drive axle event can trigger a signal to
the transmission and engine ECU or a
signal on the J1939 data link
• Automatic traction control (ATC) will limit
wheel slip under acceleration
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WARNING
Differential braking can cause a truck to
drive off a jack stand if only one drive axle
wheel end is lifted off the ground and the
driveline is operated. Traction control must
also be disabled if truck is operated on a
dyno.
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Advanced ABS Features
•
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Steering wheel angle sensor
Air application pressure sensor
Air suspension pressure sensor
Yaw rate sensor
Lateral acceleration sensor
VORAD – Vehicle onboard radar
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Advanced Air ABS Sensors
Figure 15-24 Advanced air ABS sensors.
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ABS Warning Lamp
• FMVSS 121 requires an amber-colored
ABS warning lamp in clear view of the
operator
• Three methods of controlling ABS warning
lamp:
1) Direct control by ECU
2) Control by fail safe relay
3) Controlled by J1939 data link with a J1939
multiplexed IPC
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Direct-Wired ABS Warning Lamp
Figure 15-27 Direct-wired ABS warning lamp.
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Fail Safe Relay Used to Control
ABS Warning Lamp
Figure 15-27 Direct-wired ABS warning lamp.
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Diagnosing ABS Systems
• Most Meritor-Wabco ABS ECS use
warning lamp to retrieve DTCs
• Some Bendix systems use a blink code
switch
• Bendix remote diagnostic unit (RDU) can
be plugged into the 9-pin diagnostic
connector
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Blink Codes Displayed Using ABS
Warning Lamp
Figure 15-30 Blink codes displayed using ABS warning lamp flash sequence.
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Bendix RDU
Figure 15-31 Bendix remote diagnostic unit (RDU).
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Trailer ABS
• All trailers built after March 1, 1989 are
required to have ABS
• Power to the trailer ABS is provided
through pin 7 of the J560 trailer socket
• Trucks and trailer built after March 1, 2001
are required to have a trailer ABS warning
lamp on ICP of truck
• PLC – Power line carrier
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PLC Signal Generated by
Trailer ABS ECU
Figure 15-32 Power line carrier (PLC) signal generated by trailer ABS ECU.
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Tech Tip
A problem with the trailer ABS power
supply circuit may cause the trailer ABS
warning lamps to flash when the service or
trailer brakes are applied.
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Hydraulic ABS Systems
• Required on all trucks built after March 1,
1999
• Functions similar to air ABS systems
• Hydraulic fluid is returned to the reservoir
during an ABS event
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Hydraulic ABS System
Figure 15-33 Hydraulic ABS system.
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Hydraulic ABS Disc Brake Rotor
Figure 15-34 Hydraulic ABS disc brake rotor with cast tone wheel.
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Hydraulic Power Brakes
• Uses two electric pump motors to charge gas
filled accumulators with brake fluid under
pressure
• HCU – Hydraulic compact unit
• The HPB system is connected to the J1939
data link
• Accumulator pressure is maintained at
approximately 2320 psi
• If pressure drops below 1523 a low pressure
lamp illuminates
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WARNING
Never attempt to drive a vehicle with HPB
that has the brake warning lamp
illuminated. You may not be able to stop
the vehicle.
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Hydraulic Power Brakes
(continued)
• Ignition off, vehicle not moving, service
brakes released, unit will go into sleep mode
• If ignition is turned on or brake pressed,
system will wake and control pump motors as
needed
• SAHR – Spring-applied hydraulically released
parking brake
• Meritor-WABCO Toolbox™ is the EST used
to diagnose the HPB system
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WABCO HPB SAHR Park Brake
Figure 15-35 Wabco HPB spring-apply hydraulic-release (SAHR) park brake.
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Twisted Wiring for ABS Speed
Sensors and Modulators
Figure 15-36 Twisted wiring for ABS wheel-speed sensors and modulators.
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Electronic On Board Data Reader
(EOBR)
Figure 15-37 Electronic on-board recorder (EOBR).
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Satellite Link Between Truck/Trailer
and Fleet Management
Figure 15-38 Satellite link between truck/trailer and fleet management.
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Hybrid Electric Trucks
• Parallel System – Internal combustion
engine is supplemented by electric motor
• Series System – Truck is propelled only by
electric motor and internal combustion
engine charges batteries
• A three-phase motor/generator is used to
propel vehicle and charge batteries
• A battery bank with up to 340V DC power
and inverter producing up to 500V AC
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WARNING
Lethal voltage levels are used in hybrid
electric systems. You should not attempt
to work on the high-voltage components of
an HEV until you have had proper training
and have all of the proper protective
equipment including insulated gloves.
High-voltage wiring is identified by orangecolored insulation. Never splice into this
high-voltage wiring.
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Online Service Information
Systems (SYS)
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Caterpillar Service Information System
Cummins QuickServe Online
Mack Trucks Electrical Information System
Navistar Service Information
Paccar DAVIE and ServiceNet
Volvo IMPACT
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J1939 Bus Type Network
Figure 15-42 J1939 bus-type network.
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J1939 Data Link
Figure 15-43 J1939 data link modeled as a pair of wires with two 120Ω resistors in parallel.
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Damaged J1939
Figure 15-44 Damaged J1939 data link will act as two separate networks.
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Summary
• Allison electronic automatic transmissions
use three variable reluctance speed
sensors to measure engine, turbine, and
output speeds. The transmission ECU
controls a series of normally open and
closed solenoids using PWM. These
solenoids control the flow of transmission
fluid to apply clutches for specific ranges.
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Summary (continued)
• Eaton automated manual transmissions
(AMTs) use two electric motors to activate
the shift mechanism. AMTs are divided into
two- and three-pedal systems, indicating if
the clutch is controlled by the operator or
the transmission ECU. Inputs to the ECU
include three speed sensors and rail and
gear select positions.
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Summary (continued)
• Air ABS systems use wheel-speed sensors to
determine if a wheel lock up is occurring or is
about to occur. The ABS ECU then controls
modulators to block air flowing to the brake
chambers and exhaust air out of the brake
chambers to prevent wheel lock up.
• Testing wheel-speed sensors and the
associated circuits may involve raising each
wheel end and rotating the wheel by hand
while watching for the amplitude of the AC
voltage that is generated by the variable
reluctance sensor.
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Summary (continued)
• Trailer air ABS ECUs on modern trucks use
the power line carrier technique to signal the
truck or tractor ABS ECS that a trailer ABS
fault is active. A variable frequency signal is
placed onto the 12V power supply by the
trailer ABS ECU. This signal is detected by
the truck ABS ECU in its 12V power supply,
causing the truck ABS ECU to energize the
trailer ABS warning lamp on the truck’s
instrument panel.
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Summary (continued)
• Electronic on-board recorders (EOBRs) are
electronic truck operator log books designed to
record the hours of service (HOS) for each truck
operator.
• In a parallel hybrid system, a diesel engine and
electric motor/generator are coupled together. The
electric motor is used to supplement the diesel
engine. In a series hybrid system, the electric motor
alone is used to propel and the engine is used as a
generator for the electric motor. A dual-mode hybrid
system acts as a series hybrid system during
acceleration and a parallel hybrid system at higher
speeds.
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