Electronic Brake Control Module: Description and Operation

Fig.3 RWAL Cab:

CONTROLLER ANTILOCK BRAKE
The Controller Antilock Brakes (CAB) is a microprocessor which handles testing, monitoring and controlling the ABS brake system operation. The CAB functions are:
- Perform self-test diagnostics.
- Monitor the RWAL brake system for proper operation.
- Control the RWAL valve solenoids.

Fig.4 CAB/HCU:

The CAB is mounted on the top of the hydraulic control unit. The CAB operates the ABS system and is separate from other vehicle electrical circuits. CAB voltage source is through the ignition switch in the RUN position.

NOTE: If the CAB needs to be replaced, the rear axle type and tire revolutions per mile must be programed into the new CAB. For axle type refer to Group 3 Differential and Driveline. For tire revolutions per mile,(Refer to TIRES/WHEELS/TIRES - SPECIFICATIONS). To program the CAB refer to the Chassis Diagnostic Manual.

SYSTEM SELF-TEST
When the ignition switch is turned-on the microprocessor is tested. If an error occurs during the test, a DTC will be set into the memory However it is possible the DTC will not be stored in memory if the error has occurred in the module were the DTC's are stored.

The CAB contains a self check program that illuminates the ABS warning light when a system fault is detected. Faults are stored in memory and are accessible with the DRBIII scan tool.

ABS faults remain in memory until cleared, or until after the vehicle is started approximately 50 times. Stored faults are not erased if the battery is disconnected.

CAB INPUTS
The CAB continuously monitors the speed of the vehicle by monitoring signals generated by the rear wheel speed sensor. The CAB determines a wheel locking tendency when it recognizes the axle is decelerating too rapidly.

The CAB monitors the following inputs to determine when a wheel locking tendency may exists:
- Rear Wheel Speed Sensor
- Brake Lamp Switch
- Brake Warning Lamp Switch
- Reset Switch
- 4WD Switch (If equipped)

CAB OUTPUTS
The CAB controls the following outputs for antilock braking and brake warning information:
- RWAL Valve
- ABS Warning Lamp
- Brake Warning Lamp

TRW EBC 125 CONTROLLER ANTILOCK BRAKE (CAB)
The CAB is mounted directly to the hydraulic control unit (HCU) that includes a microprocessor and two solenoids that control the valves that control brake pressure during RWAL braking. The CAB also has circuits that monitor the following:
- Monitor the brake switch input to tell whether or not to prepare for possible antilock braking
- Monitor the brake fluid level switch input to tell whether or not the state of the hydraulics has a problem
- Monitor the wheel speed sensor input to determine when a rear wheel is tending to lock up
- Operate the integral hydraulic control unit (HCU) during antilock braking based on comparing the speed sensor to information programmed in memory.
- Detect RWAL system related problems and take diagnostic action
- Able to execute self-tests and output control commands

TRW EBC 325 CONTROLLER ANTILOCK BRAKE (CAB)
The CAB is mounted directly to the hydraulic control unit (HCU) and includes a microprocessor and six solenoids that control brake pressure during antilock braking. The CAB also has circuits that monitor the following:
- Brake switch input is monitored to determine whether or not to prepare for possible ABS braking
- Monitor the brake fluid level switch input to tell whether or not the state of the hydraulics has a problem
- Wheel speed sensors are monitored to determine when a wheel is tending to lock up. The CAB will operate the valves in the HCU to control braking pressure during ABS braking.
- Detect ABS system related problems and take diagnostic action
- Able to execute self-tests and output control commands