The solid-state control unit computes the rotating speed of the wheels by the signal current sent from each sensor. When impending lock-up is detected, the ECU signals the actuator solenoids to move to predetermined positions to control brake fluid pressure to the wheels. The ECU also controls the ON/OFF. operation of the solenoid valve relay and the pump relay.
The ECU constantly monitors the function of components within the system. If any electrically detectable fault occurs, the control unit will illuminate the dashboard warning light to alert the operator. When the dash warning lamp is lit, the ABS system is disabled. The vehicle retains its normal braking capabilities without the benefit of anti-lock.
If an electrical fault is found, the ECU will assign and store a diagnostic or fault code. The code may be read and used for system diagnosis. The later model vehicles have the capability of storing up to 3 codes. If more than one fault occurs on any other vehicles, the system will only store one code and the vehicle must be road tested after repairs to allow any remaining fault to be identified.
The are no provisions for testing the ECU in the field. Proper diagnosis of a problem with the ECU, requires testing of all associated components, within the suspected circuit. By ruling out potential components and wiring circuits, the ECU can be determined to be the cause of a suspected problem.
It is important to follow all proper troubleshooting procedures before suspecting a faulty ECU.
REMOVAL & INSTALLATION
See Figures 1 and 2
The ECU is located behind the right kick panel. Remove the panel and ECU. Make sure the multi-connector is tight before going any further.
- Turn the ignition switch to the OFF position.
- Disconnect the negative battery cable.
- Remove the right front kick panel.
- Remove the nut and bolt holding the ECU to the body. Note the ground lug on the bolt.
- Lift the ECU away from the body. Release any retainers on the multi-pin connector and separate the connector from the ECU.
- Remove the ECU from the vehicle.
- Position the ECU in the vehicle and connect the multi-pin connector.
- Secure the ECU in place with the retaining nut. Attach the ground lug to the bolt before installing the retaining bolt.
- Install the right side kick panel.
- Connect the negative battery cable.
- Check ABS light operation and verify proper operation.