Visual Inspection

GENERAL
Before disconnecting any control module, make sure the ignition is "off". Failure to do so could damage the module.

When testing voltage or continuity at any control module, use the terminal side (not the wire end) of the connector. Do not probe a wire through the insulation, this will damage it and eventually cause it to fail because of corrosion.

Be careful when performing electrical tests so as to prevent accidental shorting of terminals. Such mistakes can damage fuses or components. Also, a second code could be set, making diagnosis of the original problem more difficult.

ROAD TESTING A COMPLAINT VEHICLE
Some complaints will require a test drive as part of the repair verification procedure. The purpose of the test drive is to try to duplicate the diagnostic code or symptom condition.

WARNING: BEFORE ROAD TESTING A VEHICLE, BE SURE THAT ALL COMPONENTS ARE REASSEMBLED. DURING THE TEST DRIVE, DO NOT TRY TO READ THE DRB III SCREEN WHILE IN MOTION. DO NOT HANG THE DRB FROM THE REAR VIEW MIRROR OR OPERATE IT YOURSELF HAVE AN ASSISTANT AVAILABLE TO OPERATE THE DRB.

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, which is located under the dash to the left of the steering column. If the DRB does not power up, check the power and ground supplies to the connector.
3. Turn the ignition on. Select "Antilock Brakes". If the DRB III displays "No Response" condition you must diagnose that first.
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 by locating the matching test , found under Testing and Inspection, 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, perform the proper test by locating the matching test in the Table of Contents and begin to diagnose the symptom. If a problem exists with the yellow "ABS" warning indicator or the red "Brake" indicator exists, refer to the proper tests by locating the matching test found under Testing and Inspection, Procedures and begin to 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 by locating the matching test, found under Testing and Inspection, and begin to diagnose the symptom.
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, tone 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