The anti-lock brake system (ABS) is an electronically controlled all wheel brake control system. The system is designed to retard wheel lockup during periods of high wheel slip when braking. Retarding wheel lockup is accomplished by modulating fluid pressure to the wheel brake units. When the control module detects a variation in voltage across the wheel speed sensors, the ABS is activated. The control module opens and closes various valves located inside the hydraulic anti-lock actuator assembly. These valves, called dump and isolation valves, modulate the hydraulic pressure to the wheels by applying and venting the pressure to the brake fluid circuits. The ABS does not function during normal braking applications.
The ABS module performs system tests and self-tests during startup and normal operation. The valves, wheel sensors, and fluid level circuits are monitored for proper operation. If a fault is found, the ABS will be de-activated and the amber anti-lock brake (ABS) warning light will be lit until the ignition is turned off. When the light is lit, the diagnostic trouble code (DTC) may be obtained. Under normal operation, the light will stay on for about three seconds when the ignition switch is turned to the ON position.
To retrieve ABS diagnostic trouble codes, use the following procedure:
- Turn the ignition switch to the OFF position.
- Connect one end of a jumper wire to pin 4 of the factory data link connector, located behind the fuse panel cover.
- Connect the other end of the jumper wire to a suitable ground.
- Turn the ignition switch to the ON position.
- After approximately three seconds, the ABS warning light will begin to flash. The number of flashes will indicate the codes. The light will flash once, pause, then flash twice. This start code, 12, will be repeated three times. The next series of flashes will be any stored diagnostic trouble codes. If there are no codes stored, code 12 will continue to be repeated.
After the necessary repairs have been completed, the ABS diagnostic trouble codes can be erased using the following procedure:
- Perform the ABS code retrieval procedure listed above.
- With the ignition switch still in the ON position, disconnect the jumper wire from ground.
- Reconnect the end of the jumper wire to ground three times within ten seconds, leaving it grounded for at least one second each time.
- Turn the ignition switch OFF and disconnect the jumper wire.