System Components

SYSTEM COMPONENTS
^ controller antilock brake (CAB)
^ vacuum booster
^ master cylinder
^ ABS integrated control unit hydraulic control unit (HCU), valve block assembly: 8 valve solenoids (4 inlet valves, 4 outlet valves, 2 accumulators) 1 motor, 2 pump
^ ABS integrated control unit with traction control same as above but has 10 valve solenoids.
^ 2 proportioning valves (LR, RR)
^ 4 wheel speed sensor/tone wheel assemblies
^ ABS warning indicator
^ fuses and wiring harness
^ fluid reservoir

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. On JX bodies, the ABS warning indicator is controlled by the CAB. If the 25 way CAB connector is not connected, the BCM will not receive a message from the CAB via the CCD bus and the BCM will send a message to the instrument cluster to turn on the ABS warning indicator.
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 indicator to come on.

Controller Antilock Brake (CAB)
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 compared 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 brake during antilock stop
^ monitor the system for proper operation
^ provide communication to the DRB while in diagnostic mode
^ store diagnostic information in non-volatile memory
The CAB continuously monitors the speed of each wheel. When a wheel locking tendency is detected, the CAB will command the appropriate valve to modulate brake fluid pressure in its hydraulic unit. Brake pedal position is maintained during an antilock stop by being a closed system with the use of 2 accumulators. The CAB continues to control pressure in individual hydraulic circuits until a wheel locking tendency is no longer present. The CAB turns on the pump motor during an antilock stop.
The antilock brake system is constantly monitored by the CAB for proper operation. If the CAB detects a system malfunction, it can disable the antilock system and turn on the ABS warning indicator. If the antilock function is disabled, the system will revert to standard base brake system operation.
The CAB inputs include the following:
^ ABS warning indicator
^ diagnostic communication
^ four wheel speed sensors
^ ignition switch
^ fused B+
^ brake switch
^ traction control switch
The CAB outputs include the following:
^ ABS warning indicator actuation
^ voltage
^ eight valves
^ ten valves with traction control
^ diagnostic communication
^ body controller communication
^ traction control lamp illumination

Hydraulic Control Unit
The hydraulic control unit (HCU) contains the valve block assembly, two accumulators, and pump/ motor assembly. On a JX Body the HCU is mounted on the cross member over the steering gear on the right side.
Valve Block Assembly: The valve block assembly contains valves with four inlet valves and four outlet valves. The inlet valves are spring loaded in the open position and the outlet valves are spring loaded in the closed position. During an antilock stop, these valves are cycled to maintain the proper slip ratio for each wheel. If a wheel detects slip, the inlet valve is closed to prevent and further pressure increase. Then the outlet valve is opened to release the pressure to the accumulators until the wheel is no longer slipping. Once the wheel is no longer slipping, the outlet valve is closed and the inlet valve is opened to reapply pressure. If the wheel is decelerating within its predetermined limits (proper slip ratio), the inlet valve will close to hold the pressure constant. On JX Bodies which are equipped with a traction control system, there are two additional valves that isolate the master cylinder and rear wheels. During a traction control situation the brakes are applied to reduce wheel slippage.
Pump Motor Assembly: The pump motor assembly provides the extra amount of fluid needed during antilock braking. The pump is supplied fluid that is released to the accumulators when the outlet valve is opened during an antilock stop. The pump is also used to drain the accumulator circuits after the antilock stop is complete. The pump is operated by an integral electric motor. This DC-type motor is controlled by the CAB. The CAB may turn on the pump motor when an antilock stop is detected. The pump continues to run during the antilock stop and is turned off after the stop is complete. Under some conditions, the pump/motor will run to drain the accumulators during the next drive off. The pump mechanism consists of two opposing pistons operated by an eccentric camshaft secondary hydraulic circuit. In operation, one piston draw fluid from the accumulators. The opposing piston pumps fluid to the valve body solenoids. The CAB monitors the pump/motor operation internally.
Accumulators: The accumulators provide temporary fluid storage during an antilock stop and are drained by the pump/motor. Each of the diagonal circuits uses a 3cc. accumulator.

Switches/Sensors
Master Cylinder: The master cylinder is a standard tandem compensation port design for ABS and non ABS systems. Traction control vehicles use a dual center port master cylinder. For proper traction control operation the standard master cylinder must not be used.
A fluid level switch is located in the master cylinder fluid reservoir. The switch closes when a low fluid level is detected. The fluid level switch turns on the brake warning indicator by grounding the indicator circuit. This switch does not disable the ABS system.
Wheel Speed Sensors and Tone Wheels: One Wheel Speed Sensor (WSS) is located at each wheel and sends a small AC signal to the control module (CAB). This voltage is generated by magnetic induction when a toothed sensor ring (tone wheel) passes by a stationary magnetic sensor (wheel speed sensor). The CAB converts the AC signals into digital signals for each wheel.
The front wheel speed sensor is attached to a boss in the steering knuckle. The tone wheel is an integral part of the front axle shaft. On JX Bodies the rear sensors are mounted to the rear brake backing plates or rear disc adapters. The rear tone wheels is pressed on the rear hub. The wheel speed sensor air gap is not adjustable. Refer to Specifications for wheel speed sensor air gap and resistance specifications.
The four wheel speed sensors are serviced individually. The front tone wheels are serviced as an assembly with the outer C.V, joint housing. The rear tone wheels are serviced as an assembly.
Correct antilock system operation is dependent on tone wheel speed signals from the wheel speed sensors. The vehicle's wheels and tires should all be the same size and type to generate accurate signals. In addition, the tires should be inflated to the recommended pressures for optimum system operation. Variation in wheel and tires size or significant variations in inflation pressure can produce inaccurate wheel speed signals; however, the system will continue to function when using the mini-spare.