Controller Antilock Brake: Operation: Notes

The primary functions of the contoller antilock brake (CAB) are to:

1. monitor the antilock brake system for proper operation.
2. detect wheel locking or wheel slipping tendencies by monitoring the speed of all four wheels of the vehicle.
3. control fluid modulation to the wheel brakes while the system is in an ABS mode.
4. store diagnostic information.
5. provide communication to the DRBIII® scan tool while in diagnostic mode.

The CAB constantly monitors the antilock brake system for proper operation. If the CAB detects a fault, it will send a message to the mechanical instument cluster (MIC) instructing it to turn on the amber ABS warning indicator lamp and disable the antilock braking system. The normal base braking system will remain operational.

The CAB continuously monitors the speed of each wheel through the signals generated by the wheel speed sensors to determine if any wheel is beginning to lock. When a wheel locking tendency is detected, the CAB commands the CAB command coils to actuate. The CAB command coils then open and close the valves in the HCU that modulate brake fluid pressure in some or all of the hydraulic circuits. The CAB continues to control pressure in individual hydraulic circuits until a locking tendency is no longer present.

The CAB contains a self-diagnostic program that monitors the antilock brake system for system faults. When a fault is detected, the amber ABS warning lamp is turned on and the fault diagnostic trouble code (DTC) is then stored in a diagnostic program memory. These DTC's will remain in the CAB memory even after the ignition has been turned off. The DTC's can be read and cleared from the CAB memory by a technician using the DRB scan tool. If not cleared with a DRB scan tool, the fault occurrence and DTC will be automatically cleared from the CAB memory after the identical fault has not been seen during the next 3,500 miles of vehicle operation.