ABS System Self-Diagnosis

ABS SELF-DIAGNOSIS
The ABS system is equipped with a self-diagnosis capability, which may be used to assist in the isolation of ABS faults. The features are described below.

START-UP CYCLE
The self-diagnosis ABS start-up cycle begins when the ignition switch is turned to the ON position. Electrical checks are completed on ABS components, including the CAB, solenoid continuity, and the relay system operation. During this check the amber ABS warning lamp is turned on for approximately 5 seconds and the brake pedal may emit a popping sound, moving slightly when the solenoid valves are checked.

DRIVE-OFF CYCLE
The first time the vehicle is set in motion after an ignition off/on cycle, the drive-off cycle occurs. This cycle is performed when the vehicle reaches a speed of approximately 20 kph (12 mph.).
- The pump/motor is briefly activated to verify function. When the pump/motor is briefly activated, a whirling or buzzing sound may be heard by the driver. This sound is normal, indicating the pump/ motor is running.
- The wheel speed sensor output correct operating range is verified.

ONGOING TESTS
While the system is operating, these tests are performed on a continuous basis:
- solenoid continuity
- Wheel speed sensor continuity
- wheel speed sensor output