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 DRBIII to the data link connector, which is located under the dash to the left of the steering column. If the DRBIII does not power up, check the power and ground supplies to the connector.
3. Turn the ignition on. Select "Antilock Brakes". If the DRBIII displays "No Response" condition you must diagnose that first.
4. Read and record all ABS Diagnostic Trouble Codes (DTC's). If the "CAB Power Feed Circuit" diagnostic trouble code is present, it must be repaired prior to addressing other DTC's. If any additional DTC's are present, proceed to the appropriate test by locating the matching test in the Table of Contents and begin to diagnose the symptom.
5. If there are no diagnostic trouble codes present, identify the customer complaint, select "Inputs/ Outputs" and read the brake switch input as you press and release the brake pedal. If the display does not match the state of the pedal, diagnose the symptom. If a problem exists with the amber "ABS" warning indicator or the red "Brake" indicator, diagnose the symptom. Read the traction control switch input as you press and release the switch. If the display does not match the state of the indicator, diagnose the symptom.
6. If no other problems are found, it will be necessary to road test the vehicle. Perform several antilock stops from above 50 Km/h (30 mph) and then repeat step 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 25 Km/h (15 mph) or 40 Km/h (24 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, to one wheel condition, and/or brakes hanging up are possible causes of this condition.
9. After a road test and no problems were found, refer to any Technical Service Bulletins that may apply.