Antilock Brakes / Traction Control Systems: Description and Operation

Special Tools:

Anti-Lock Control
The anti-lock-brake system (ABS) control module receives wheel speed readings from each wheel speed sensor and processes this information to determine if an ABS event is necessary. The wheel speed sensor electrically senses each tooth of the wheel speed sensor indicators as it passes through the wheel speed sensors magnetic field.

The ABS control module continuously monitors and compares the rotational speed of each wheel and when it detects an impending wheel lock, modulates brake pressure to the appropriate brake caliper. This is accomplished by triggering the hydraulic control unit (HCU) to open and close the appropriate solenoid valves. Once the affected wheel returns to normal speed, the ABS control module returns the solenoid valves to their normal position, and normal (base) braking resumes.

The ABS control module is self monitoring. When the ignition switch is turned to the RUN position, the ABS control module will do a preliminary electrical check, and at approximately 20 km/h (12 mph) the pump motor is turned on for approximately one half-second. Also, during all phases of operation the ABS control module (after the vehicle is in motion) checks for correct operation of the wheel speed sensors. Any malfunction of the ABS will cause the ABS to shut off. Normal power assisted braking, however, remains.

The ABS control module has the ability to store three DTCs in its memory.

The traction control system controls wheel spin by modulating the engine torque by communicating to the powertrain control module (PCM) and by applying, then releasing, the appropriate brake to restore traction when one or both drive wheels lose traction and begin to spin during acceleration.

The traction control system can be disabled by depressing the traction control switch and is indicated by an LED in the traction control switch. The traction control will reset and return to normal traction assist when the ignition switch is cycled or when the traction control switch is depressed.