Principles of Operation

NOTE: The Antilock Brake System is NOT available without integral Traction Control System.

Special Tools:

The 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 ABS sensor indicators as it passes through the wheel speed sensor's magnetic field.

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 also the first time the vehicle reaches approximately 16 km/h (10 mph) after the ignition switch is turned on, the pump motor is turned on for approximately one half second. Any malfunction of the system will cause the anti-lock brake system to shut off, however normal power assisted braking remains.

The ABS control module continuously monitors and compares the rotational speed of each wheel, and only when it detects an impending wheel lock, modulates brake pressure to the appropriate brake. 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 has the ability to store multiple diagnostic trouble codes (DTCs) in memory.

The traction control system controls wheel spin by modulating the engine torque and by applying the driven wheel brakes. The traction control module communicates desired engine torque to the powertrain control module (PCM), which then reduces engine torque by controlling ignition and fuel delivery, 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. The traction control system will reset and return to normal traction assist when the ignition switch is cycled, or the traction control switch is depressed again.

If the traction control system is in operation continually on slippery roads, the ABS control module may disable the brake portion of the system to prevent overheating of the system (cool down period). When the cool down period expires, the brake portion of the traction control is restored (anti-lock braking is fully functional during the cool down period).