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8E - 4
ELECTRONIC CONTROL MODULES
COMMUNICATION (Continued)
ule. The CCD error message is a default message
used by the DRBIII
whether or not the PCI Bus is operational. The mes-
sage is only an indication that a module is either not
responding or the vehicle is not equipped.
CONTROLLER ANTILOCK
BRAKE
DESCRIPTION
The controller antilock brake (CAB) is a micropro-
cessor-based device which monitors the antilock
brake system (ABS) during normal braking and con-
trols it when the vehicle is in an ABS stop. The CAB
is mounted to the HCU as part of the integrated con-
trol unit (ICU) (Fig. 3). The CAB uses a 47-way con-
nector on the vehicle wiring harness. The power
source for the CAB is through the ignition switch in
the RUN or ON position. The CAB is on the PCI bus.
Fig. 3 Integrated Control Unit (ICU)
1 - PUMP/MOTOR
2 - HCU
3 - CAB
OPERATION
The primary functions of the controller antilock
brake (CAB) are to:
• Monitor the antilock brake system for proper
operation.
• Detect wheel locking or wheel slipping tenden-
cies by monitoring the speed of all four wheels of the
vehicle.
• Control fluid modulation to the wheel brakes
while the system is in ABS or traction control mode.
• Store diagnostic information.
and in no way indicates
• Provide communication to the DRBIII scan tool
while in diagnostic mode.
• Illuminate the amber ABS warning indicator
lamp.
• (With traction control only) Illuminate the TRAC
ON lamp in the message center on the instrument
panel when a traction control event occurs.
• (with traction control only) Illuminate the TRAC
OFF lamp when the amber ABS warning indicator
lamp illuminates.
The CAB constantly monitors the antilock brake
system for proper operation. If the CAB detects a
fault, it will turn on the amber ABS warning indica-
tor lamp and disable the antilock braking system.
The normal base braking system will remain opera-
tional.
NOTE: If the vehicle is equipped with traction con-
trol, the TRAC OFF lamp will illuminate anytime the
amber ABS warning indicator lamp illuminates.
The CAB continuously monitors the speed of each
wheel through the signals generated by the wheel
speed sensors to determine if any wheel is beginning
to lock. When a wheel locking tendency is detected,
the CAB commands the CAB solenoid coils to actu-
ate. The coils then open and close the valves in the
HCU that modulate brake fluid pressure in some or
all of the hydraulic circuits. The CAB continues to
control pressure in individual hydraulic circuits until
a locking tendency is no longer present.
The CAB contains a self-diagnostic program that
monitors the antilock brake system for system faults.
When a fault is detected, the amber ABS warning
indicator lamp is turned on and the fault diagnostic
trouble code (DTC) is then stored in a diagnostic pro-
gram memory. A latched fault will disable certain
system functionality for the current ignition cycle. An
unlatched fault will disable certain system function-
ality until the fault condition disappears. These
DTC's will remain in the CAB memory even after the
ignition has been turned off. The DTC's can be read
and cleared from the CAB memory by a technician
using the DRBIII
scan tool. If not cleared with a
DRBIII scan tool, the fault occurrence and DTC will
be automatically cleared from the CAB memory after
the identical fault has not been seen during the next
3,500 miles. Drive-off may be required for the amber
ABS warning indicator lamp to go out on the next
ignition cycle.
CAB INPUTS
• Wheel speed sensors (four)
• Brake lamp switch
• Ignition switch
• System and pump voltage
• Ground
CS
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