Anti-Lock Brake System: Diagnosis: Notes

1. Before diagnosing ABS system for fault codes, perform pre-diagnostic visual inspection to detect obvious problems. See PRE-DIAGNOSTIC INSPECTION  under DIAGNOSIS & TESTING. Repair problems as necessary.
2. Using Tech 1, read all current and history fault codes. Fault codes are stored in order of occurrence. If no fault codes are present, go to step 4). If fault codes are stored, note which codes are current and which codes are history. DO NOT clear fault codes.
3. Using Tech 1, review code history. Review fault codes stored and frequency of failure. Refer to ENHANCED DIAGNOSTICS  under DIAGNOSIS & TESTING. DO NOT clear codes until ABS repairs are complete. After reviewing ENHANCED DIAGNOSTICS, perform DIAGNOSTIC CIRCUIT CHECK under DIAGNOSTIC CHARTS  . Refer to DIAGNOSTIC TROUBLE CODES table as necessary.
4. Using Tech 1, perform automated modulator test. Automated modulator test may isolate cause of problem. If failure is intermittent and not reproducible, test drive vehicle using snapshot feature of Tech 1. Drive vehicle in a normal manner, with normal acceleration, stopping and turning.
5. If vehicle test drive does not reproduce any failures, perform another test drive. On second test drive, perform an ABS stop from about 30-50 MPH. Check snapshot feature of Tech 1 to see if any faults were set.
6. If fault codes were set, perform DIAGNOSTIC CIRCUIT CHECK under DIAGNOSTIC CHARTS  . Refer to DIAGNOSTIC TROUBLE CODES table as necessary. DO NOT clear codes until ABS repairs are complete. If no faults were set and ABS warning light and/or BRAKE warning light is on, refer to CHART A or CHART B under DIAGNOSTIC CHARTS  .