Jeep 1997 Grand Cherokee Service Manual page 218

5 - 38 BRAKES
DESCRIPTION AND OPERATION (Continued)
ACCELERATION SWITCH
The acceleration switch is located under the rear
seat. The switch (Fig. 4), provides an additional vehi- SWITCH PART NUMBER
cle deceleration reference during 4WD operation. The
switch is monitored by the CAB at all times. The
switch reference signal is utilized by the CAB when
all wheels are decelerating at the same speed.
Fig. 4 Acceleration Switch
ABS SYSTEM RELAYS
The ABS system has two relays, which are the
main and motor pump relays. The main relay is used
for the solenoid valves and CAB. The main relay is
connected to the CAB at the power control relay ter-
minal. The motor pump relay is used for the motor
pump only. The pump motor relay starts/stops the
pump motor when signaled by the CAB.
ABS WARNING LAMP
The amber ABS warning lamp is located in the
instrument cluster. The lamp illuminates at start-up
to perform a self check. The lamp goes out when the
self check program determines the system is operat-
ing normal. If an ABS component exhibits a fault the
CAB will illuminate the lamp and register a trouble
code in the microprocessor. The lamp is controlled by
the CAB. The CAB controls the lamp by directly
grounding the circuit.
DIAGNOSIS AND TESTING
ANTILOCK BRAKES
The ABS brake system performs several self-tests
every time the ignition switch is turned on and the
vehicle is driven. The CAB monitors the systems
input and output circuits to verify the system is oper-
ating correctly. If the on board diagnostic system
senses that a circuit is malfunctioning the system
will set a trouble code in its memory.
NOTE: The MDS or DRB III scan tool is used to
diagnose the ABS system. For additional informa-
tion refer to the Antilock Brake section in Group
FRONT OF SWITCH FOR ARROW PROPER MOUNTING INDICATES
8W. For test procedures refer to the Chassis Diag-
nostic Manual.
SERVICE PROCEDURES
BLEEDING ABS BRAKE SYSTEM
ing methods plus use of the DRB scan tool. The pro-
cedure involves performing a base brake bleeding,
followed by use of the scan tool to cycle and bleed the
HCU pump and solenoids. A second base brake bleed-
ing procedure is then required to remove any air
remaining in the system.
brake section for procedure.
CELLANEOUS, then ABS BRAKES. Follow the
instructions displayed. When scan tool displays TEST
COMPLETE, disconnect scan tool and proceed.
Refer to base brake section for procedure.
proper brake operation before moving vehicle.
REMOVAL AND INSTALLATION
HYDRAULIC CONTROL UNIT/CONTROLLER
ANTILOCK BRAKES
REMOVAL
tery.
and move the reservoir to the side.
remove connector (Fig. 5).
6).
assembly.
INSTALLATION
tighten mounting nuts to 12 N·m (9 ft. lbs.).
ABS system bleeding requires conventional bleed-
(1) Perform base brake bleeding. Refer to base
(2) Connect scan tool to the Data Link Connector.
(3) Select ANTILOCK BRAKES, followed by MIS-
(4) Perform base brake bleeding a second time.
(5) Top off master cylinder fluid level and verify
(1) Remove negative battery cable from the bat-
(2) Remove air cleaner housing.
(3) Remove windshield reservoir mounting bolts
(4) Remove steering gear shield.
(5) Pull CAB harness connector release out and
(6) Remove the brake lines from the HCU.
(7) Remove HCU/CAB bracket mounting nuts (Fig.
(8) Remove HCU/CAB assembly from the vehicle.
(9) Remove bracket bolts from the HCU/CAB
(1) Install bracket onto the HCU/CAB assembly.
(2) Install HCU/CAB assembly in the vehicle and
ZG