Electronic Brake Control Module: Description and Operation
MODULE-ANTILOCK BRAKEDESCRIPTION
The Antilock Brake Module (ABM) 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 or when in a traction control situation. The ABM utilizes a 47-way electrical connector on the vehicle wiring harness. The power source for the ABM is through the ignition switch in the RUN or ON position.
The ABM (1) is mounted to the HCU (2) as part of the Integrated Control Unit (ICU). The ICU is located in the engine compartment on the inboard side of the left body frame rail.
OPERATION
The primary functions of the Antilock Brake Module (ABM) are to:
- monitor the Antilock Brake System (ABS) 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 an ABS mode or the traction control system is activated.
- store diagnostic information.
- provide communication to the scan tool while in diagnostic mode.
The ABM constantly monitors the antilock brake system for proper operation. If the ABM detects a fault, it will send a message to the mechanical instrument 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 ABM 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 ABM commands the ABM command coils to actuate. The ABM 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 ABM continues to control pressure in individual hydraulic circuits until a locking tendency is no longer present.
The ABM 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. These DTC's will remain in the ABM memory even after the ignition has been turned off. The DTC's can be read and cleared from the ABM memory by a technician using a scan tool. If not cleared with a scan tool, the fault occurrence and DTC will be automatically cleared from the memory after the identical fault has not been seen during the next 3,500 miles of vehicle operation.