Anti-Lock Brake System: Operation

NOTE: For vehicles equipped with optional traction control, see TRACTION CONTROL article.

With vehicle moving, AC signals are sent from individual wheel speed sensors to ECU. ECU monitors brakelight switch to determine when brake pedal is depressed. With brake pedal depressed, ECU uses speed sensor signals to determine vehicle deceleration.

During panic stop (as determined by ECU), ECU activates solenoid valves inside actuator. Solenoid valves are cycled to apply, release or maintain hydraulic pressure to each wheel in any combination.

An ABS warning light, located on instrument panel, illuminates for 3 seconds as a bulb test when ignition is turned on. A primary check is performed after each engine start and initial time vehicle speed exceeds 6 MPH. Actuator noise should be heard as vehicle speed exceeds 6 MPH. If brake pedal is depressed before vehicle speed exceeds 6 MPH, primary check will not occur until brake pedal is released.

During normal driving conditions, ABS functions like a standard brake system. When wheel lock-up is detected, brake pedal may pulsate and steering wheel and vehicle body may vibrate (this is normal). Pulsation or vibration will continue until ABS function is no longer needed or vehicle is stopped.

CAUTION: See ANTI-LOCK BRAKE SAFETY PRECAUTIONS article in GENERAL INFORMATION.