Controller Anti-Lock Brake: Operation
The primary functions of controller anti-lock brake (CAB) are to:
- monitor anti-lock brake system for proper operation.
- detect wheel locking or wheel slipping tendencies by monitoring speed of all four wheels of vehicle.
- control fluid modulation to wheel brakes while system is in ABS mode.
- store diagnostic information.
- provide communication to DRBIII(R) scan tool while in diagnostic mode.
The CAB constantly monitors anti-lock brake system for proper operation. If CAB detects a fault, it will turn on amber ABS warning indicator lamp and disable anti-lock braking system.
The normal base braking system will remain operational. The CAB continuously monitors speed of each wheel through signals generated by wheel speed sensors to determine if any wheel is beginning to lock. When a wheel locking tendency is detected, CAB commands CAB command coils to actuate. The CAB command coils then open and close valves in HCU that modulate brake fluid pressure in some or all of 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 anti-lock brake system for system faults. When a fault is detected, amber ABS warning lamp is turned on and fault diagnostic trouble code (DTC) is then stored in a diagnostic program memory. These DTC's will remain in CAB memory even after ignition has been turned off. The DTC's can be read and cleared from CAB memory by a technician using DRBIII scan tool. If not cleared with a DRBIII scan tool, fault occurrence and DTC will be automatically cleared from CAB memory after identical fault has not been seen during next 3,500 miles of vehicle operation.