Controller Antilock Brake (CAB)

Integrated Control Unit (ICU):

The Hydraulic Control Unit (HCU) and the Controller Antilock Brake (CAB) used with this antilock brake system are combined (integrated) into one unit, which is called the Integrated Control Unit (ICU). The ICU is located on the driver's side of the vehicle, and is mounted to the left front frame rail below the master cylinder.

The Antilock Brake System (ABS)-only ICU consists of the following components: the CAB, eight (build/decay) solenoid valves (four inlet valves and four outlet valves), valve block, fluid accumulators, a pump, and an electric motor.

The replaceable components of the ICU are the HCU and the CAB. No attempt should be made to service any individual components of the HCU or CAB.

CONTROLLER ANTILOCK BRAKE (CAB)
The Controller Antilock Brake (CAB) is a microprocessor-based device which monitors the ABS system during normal braking and controls it when the vehicle is in an ABS stop. The CAB is mounted to the bottom of the HCU. The CAB uses a 25-way electrical connector on the vehicle wiring harness. The power source for the CAB is through the ignition switch in the RUN or ON position. The CAB is on the PCI bus.

The primary functions of the (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 DRB 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 turn on the amber ABS warning 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 Antilock Brake System (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 255 key cycles of vehicle operation.

CONTROLLER ANTILOCK BRAKE INPUTS
- wheel speed sensors (four)
- stop lamp switch
- ignition switch
- system relay voltage
- ground.
- diagnostic communication (PCI)

CONTROLLER ANTILOCK BRAKE OUTPUTS
- amber ABS warning lamp actuation.
- diagnostic communication. (PCI)