Traction Control: Anti-Lock: Operation

Wheel sensors located at each wheel send an AC electrical signal to the ABS Electronic Control Unit/Hydraulic Unit (ABS ECU/HU). The ABS ECU/HU translates this information as wheel speed. When decelerating wheel speed rate is determined to be excessive in comparison to other monitored wheels, the hydraulic unit cycles hydraulic brake pressure to each wheel to equalize speed of all wheels. ABS turns off when vehicle reaches 4 MPH. Minor lock-up may occur at this point.

With engine running and vehicle speed more than 4 MPH, pump motor will operate for a short period of time and may be heard inside vehicle. During pump motor operation, ABS system completes a self-check. During ABS system operation, brake pedal pulsation and steering wheel and vehicle body vibration may be experienced. These conditions are normal. During normal operation, the ABS makes several sounds that may seem unusual at first:

• A whining sound is caused by the ABS hydraulic unit motor.
• When pressure is applied to the brake pedal, pulsation of the pedal causes a scraping sound.
• When brakes are applied firmly, the ABS operates, rapidly applying and releasing the brakes many times per second. This repeated application and release of braking forces can make a thumping sound and the tires to squeak.

When braking on loose surfaces like snow-covered or gravel roads, the stopping distance can be longer for an ABS-equipped vehicle than the stopping distance for a vehicle with a conventional brake system. A shock may be felt when the brake pedal is lightly pressed while driving at a low speed. This is a normal characteristic because the ABS system operation check is carried out when vehicle speed is less than 5 mph.