Test 1A: Checking System For Faults
NOTE:
Perform PRE-DIAGNOSTIC INSPECTION
before proceeding.
- Perform a visual inspection of ABS system components, wiring harnesses and connectors. Repair obvious problems before continuing. Verify brakelights are operational. Repair brakelights as necessary before continuing.
- Connect scan tool to Data Link Connector (DLC). If scan tool displays NO RESPONSE, perform TEST 22A: NO RESPONSE . If scan tool does not display NO RESPONSE, go to next step.
- Read and record all ABS Diagnostic Trouble Codes (DTCs). If DTC VALVE POWER FEED CIRCUIT is set, perform TEST 19A: VALVE BLOCK FEED FAILURE . DTC VALVE POWER FEED CIRCUIT must be repaired before diagnosing other DTCs.
- If no DTCs are present, select INPUTS/OUTPUTS on scan tool. Read brake switch input as brake pedal is pressed and released. If scan tool display does not match brake pedal position, perform TEST 21A: BRAKE SWITCH CIRCUITS . If scan tool display matches brake pedal position, go to next step.
- If a problem exists with Amber ABS warning light or Red BRAKE light, perform appropriate test under SYSTEM TESTS in DIAGNOSTIC TROUBLE CODE IDENTIFICATION
table. If no problem exists with warning lights, go to next step.CAUTION: Scan tool must be disconnected before road testing vehicle. Anti-lock brake system is disabled when in diagnostic mode.
- Disconnect scan tool from DLC. Road test vehicle. Scan tool MUST be disconnected before road testing vehicle. Perform several ABS stops from more than 30 MPH, then repeat steps 2 and 3). If any DTCs are set, perform appropriate test(s).
- During test drive the following conditions are normal and no repairs should be attempted to correct these conditions.
- Slight brake pedal drop and a pop noise when ignition is initially turned on.
- When vehicle is first driven off, a humming sound may be heard and/or felt when vehicle reaches approximately 7 MPH.
- Groaning, popping and/or ticking may be heard inside passenger compartment during an ABS stop.
- Brake pedal feedback (clicking and vibrating) during ABS stop.
- Brake pedal ratcheting down at end of an ABS stop.
- If complaint is ABS cycling at the end of a stop at low vehicle speeds, it may be caused by a marginal wheel speed sensor signal. Brakes hanging up, sensor air gap or tone wheel condition are possible causes of ABS cycling at the end of a stop at low vehicle speeds. After road test, if no problems are identified, check if any Technical Service Bulletins (TSBs) apply to vehicle.
DIAGNOSTIC TROUBLE CODE IDENTIFICATION