Table of Contents
Advertisement
GENERAL INFORMATION
slip by braking the wheel that is losing traction.
The system is designed to operate at speeds below
56 km/h (35 mph).
The controller antilock brake (CAB) monitors
wheel speed. If during acceleration the CAB detects
front (drive) wheel slip and the brakes are not
applied, it will enter traction control mode. The
CAB performs the traction control function in the
following sequence:
1. Closes the (normally open) isolation valves.
2. Starts pump/motor to supply volume/pressure to
front hydraulic circuits (pump runs continuously
during traction control).
3. Opens and closes build and decay valves to
maintain minimum wheel slip and maximum
traction.
The cycling of the build and decay valves works
similarly to ABS except that they work to control
wheel spin by applying brakes. ABS function is to
control wheel skid by releasing brakes.
Two pressure relief valves allow pressure/volume
to return to the reservoir when not consumed by the
build/decay cycles. These are required because the
pump supplies more volume than the system re-
quires.
If at any time the brakes are applied during a
traction control cycle, the brake switch will trigger
the CAB to switch off the traction control.
The traction control system will be enabled at
each ignition cycle. It may be turned off by depress-
ing the traction control switch. The traction control
system function indicator will illuminate immedi-
ately upon depressing the traction control switch
button. The indicator will flash during a traction
control cycle. If the controller calculates that the
brake temperatures are high, the traction control
system will become inoperative until a time-out
period has elapsed. When in this thermo protection
mode, the traction control indicator will illuminate;
however, a fault will not be registered.
3.3 SYSTEM COMPONENTS
•
controller antilock brake (CAB)
•
vacuum booster
•
master cylinder
•
ABS integrated control unit hydraulic control
unit (HCU), 1 motor pump.
•
ABS integrated control unit with traction control
same as above but has 10 valve solenoids. 2
valves are isolation valves.
•
4 wheel speed sensor/tone wheel assemblies
•
ABS warning indicator
•
fuses and wiring harness
•
fluid reservoir
•
brake lamp switch
3.3.1 ABS AND BRAKE WARNING
INDICATORS
The amber ABS warning indicator is located in
the instrument cluster. It is used to inform the
driver that the antilock function has been turned
off. The ABS warning indicator is indirectly con-
trolled by the CAB. The CAB will send a message
across the PCI Bus that informs the instrument
cluster to turn the ABS warning indicator ON or
OFF. If the 24-way CAB connector is not connected,
the instrument cluster will not receive a message
from the CAB via the PCI BUS circuit. The instru-
ment cluster will then turn on the ABS warning
indicator.
The ABS Warning Indicator will remain lit during
every key cycle until a circuit or component fault is
repaired and the CAB no longer detects the fault.
After repair of a sensor signal fault or a pump motor
fault, the CAB must sense all four wheels at 25
km/h (15 mph) before it will extinguish the ABS
Indicator.
The Instrument Cluster will illuminate the ABS
Warning Indicator if it loses communication with
the CAB.
The red BRAKE warning indicator is also located
in the instrument cluster. It can be activated in
several ways. Application of the parking brake or a
low fluid signal from the fluid level switch located in
the master cylinder reservoir will cause the indica-
tor to come on. The status of the red BRAKE
warning indicator is not monitored by the CAB.
3.3.2 CONTROLLER ANTILOCK BRAKE
(CAB)
The Controller Antilock Brake (CAB) is a
microprocessor-based device that monitors wheel
speeds and controls the antilock functions. The
CAB contains two microprocessors that receive
identical sensor signals and then independently
process the information. The results are then com-
pared to make sure that they agree. Otherwise, the
CAB will turn off the antilock and turn on the ABS
amber warning indicator.
The primary functions of the CAB are to:
•
detect wheel locking tendencies
•
control fluid pressure modulation to the brakes
during an antilock stop
•
monitor the system for proper operation
•
provide communication to the DRBIII while in
diagnostic mode
•
store diagnostic information in non-volatile
memory
2
Advertisement
Table of Contents
