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Right from the service info.....The controller antilock brake (CAB) is a microprocessor-based device which monitors the antilock brake system (ABS) during normal braking and controls it when the vehicle is in an ABS stop. The CAB is mounted to the HCU as part of the integrated control unit (ICU) (Integrated Control Unit (ICU)). The CAB uses a 47-way 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.
OPERATION
The primary functions of the controller antilock brake (CAB) are to:

Monitor the antilock brake system for proper operation.
Detect wheel locking or wheel slipping tendencies by monitoring the speed of all four wheels of the vehicle.
Control fluid modulation to the wheel brakes while the system is in ABS or traction control mode.
Store diagnostic information.
Provide communication to the DRBIII® scan tool while in diagnostic mode.
Illuminate the amber ABS warning indicator lamp.
(With traction control only) Illuminate the TRAC ON lamp in the message center on the instrument panel when a traction control event occurs.
(with traction control only) Illuminate the TRAC OFF lamp when the amber ABS warning indicator lamp illuminates.
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 indicator lamp and disable the antilock braking system. The normal base braking system will remain operational.

NOTE: If the vehicle is equipped with traction control, the TRAC OFF lamp will illuminate anytime the amber ABS warning indicator lamp illuminates.

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 solenoid coils to actuate. The 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 indicator lamp is turned on and the fault diagnostic trouble code (DTC) is then stored in a diagnostic program memory. A latched fault will disable certain system functionality for the current ignition cycle. An unlatched fault will disable certain system functionality until the fault condition disappears. 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 DRBIII® scan tool. If not cleared with a DRBIII® 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. Drive-off may be required for the amber ABS warning indicator lamp to go out on the next ignition cycle.

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Makes me wonder how I ever drove through decades of horrid Ontario winters with one brake hose and four drums and never crashed and burned wothout all this complex, troublesome crap.

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Well definetly more complicated than days of old (for me anyway)
Used to be just a stand alone module that you shorted a(yellow)wire to ground and counted the flashes from the Antiloc lamp... guess I have to take it somewhere....apcray
Thanks Todd for the info