Combination Valve; G-Switch; Abs Warning Lamp - Jeep cherokee 2000 Service Manual

XJ
DESCRIPTION AND OPERATION (Continued)
sensors have a resistance between 900 and 1300
ohms.
Fig. 2 Wheel Speed Sensors
1 – FRONT SENSOR
2 – REAR SENSOR
3 – PICKUP FACE
FRONT SENSOR AIR GAP
Front sensor air gap is fixed and not adjustable.
Only rear sensor air gap is adjustable.
Although front air gap is not adjustable, it can be
checked if diagnosis indicates this is necessary. Front
air gap should be 0.36 to 1.5 mm (0.014 to 0.059 in.). If
gap is incorrect, the sensor is either loose, or damaged.
REAR SENSOR AIR GAP
A rear sensor air gap adjustment is only needed
when reinstalling an original sensor. Replacement
sensors have an air gap spacer attached to the sensor
pickup face. The spacer establishes correct air gap
when pressed against the tone ring during installa-
tion. As the tone ring rotates, it peels the spacer off
the sensor to create the required air gap. Rear sensor
air gap is 0.92-1.275 mm (0.036-0.05 in.).
Sensor air gap measurement, or adjustment proce-
dures are provided in this section. Refer to the front,
or rear sensor removal and installation procedures as
required.

COMBINATION VALVE

DESCRIPTION
The combination valve contains a pressure differ-
ential valve and switch and a rear brake proportion-
ing valve. The valve is not repairable and must be
replaced as an assembly if diagnosis indicates this is
necessary.
OPERATION
PRESSURE DIFFERENTIAL VALVE
The pressure differential switch is connected to the
brake warning light. The switch is actuated by move-
ment of the switch valve. The switch monitors fluid
pressure in the separate front/rear brake hydraulic
circuits.
A decrease or loss of fluid pressure in either
hydraulic circuit will cause the switch valve to shut-
tle to the low pressure side. Movement of the valve
pushes the switch plunger upward. This action closes
the switch internal contacts completing the electrical
circuit to the red warning light. The switch valve will
remain in an actuated position until repairs to the
brake system are made.
PROPORTIONING VALVE
The proportioning valve is used to balance front-
rear brake action at high decelerations. The valve
allows normal fluid flow during moderate braking.
The valve only controls fluid flow during high decel-
erations brake stops.

G-SWITCH

DESCRIPTION
The G-switch is located under the rear seat. The
switch has directional arrow and must be mounted
with the arrow pointing towards the front of the
vehicle.
OPERATION
The switch (Fig. 3), provides an additional vehicle
deceleration reference during 4x4 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.

ABS WARNING LAMP

DESCRIPTION
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.
OPERATION
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 lamp is illuminated when the CAB sends a
ground signal to the ABS relay. The ABS relay then
grounds the lamp circuit and illuminates the lamp.
BRAKES 5 - 35