Diagnostic Strategies

DIAGNOSIS
1. Your diagnostic test procedure must begin with a thorough visual inspection of the ABS system for damaged components or disconnected connectors. The brake lamps must be operational, and if they are not, repair them prior to continuing.
2. Connect the DRB III to the data link connector located under the dash. If the DRB III does not power up, check the power and ground supplies to the connector.
3. Select "Antilock Brakes". Turn the ignition on. If the DRB III displays "No Response", refer to Communication in the Body Diagnostic Procedures to diagnose the symptom.
4. Read and record all ABS diagnostic trouble codes. If the "CAB Power Feed Circuit" diagnostic trouble code is present, it must be repaired prior to addressing any other DTC's. If any additional codes are present, proceed to the appropriate test.
5. If there are no diagnostic trouble codes present, select "Inputs/Outputs" and read the brake switch input as your press and release the brake pedal. If the display does not match the state of the pedal, perform the proper test. Read the "G-Sensor" status, with the vehicle on a level surface, both switches should read "CLOSED". If the status is not correct, perform the proper test. If a problem with the amber "ABS" warning indicator exists, refer to the proper test.
6. If no other problems are found, it will be necessary to road test the vehicle. THE DRB III MUST NOT BE CONNECTED TO THE DATA LINK CONNECTOR WHEN ROAD TESTING FOR PROPER ANTILOCK OPERATION. THE SYSTEM IS DISABLED WHILE IN DIAGNOSTIC MODE. Perform several antilock stops from above 50 Km/h (30 mph) and then repeat steps 2, 3, and 4. If any diagnostic trouble codes are present, proceed to the appropriate test.
7. The following conditions should be considered "NORMAL" operation, and no repairs should be attempted to correct them.
- Brake pedal feedback during an ABS stop (clicking, vibrating)
- Clicking, groaning or buzzing at 10 km/h (6 mph) (drive off self test)
- Groaning noise during an ABS stop
- Slight brake pedal drop and pop noise when ignition is initially turned on
- Brake pedal ratcheting down at the end of an ABS stop
8. If the complaint is ABS "cycling" at the end of a stop at low speeds, it may be caused by a marginal wheel speed sensor signal. The sensor air gap, tone wheel condition, and/or brakes hanging up are possible causes of this condition.
9. After a road test in which no problems were found, refer to any Technical Service Bulletins that may apply.