Pre-Diagnosis Inspection

NOTE: When servicing ABS, the following steps should be followed in order. Failure to follow these steps may result in loss of important diagnostic data and lead to difficult and time consuming diagnostic procedures.

Using Tech 1 scan tool, read all current and stored (history) Diagnostic Trouble Codes (DTCs). Do not clear DTCs. See RETRIEVING CODES . Read DTC HISTORY data. Note DTCs stored and frequency of failures. Start diagnosis with most recent malfunction.
Perform a vehicle preliminary diagnosis inspection. This should include the following:
- Check master cylinder fluid level. Check brake fluid for signs of contamination.
- Check hydraulic modulator for leaks or wiring damage.
- Check brake components at all 4 wheels. Ensure brakes apply properly and no drag exists.
- Check for worn or damaged wheel bearings.
- Check wheel speed sensors and wiring. Ensure sensors are securely attached and toothed ring is not damaged.
- Check wheel-side axle joint alignment and operation.
- Ensure tires meet manufacturers size requirements and have acceptable tread depth.
If no DTCs or mechanical component faults are present, perform DIAGNOSTIC CIRCUIT CHECK. If fault is intermittent, test drive vehicle using snapshot feature of Tech 1. Perform normal acceleration, stopping and turning maneuvers. If fault does not repeat, perform an ABS stop, on a low coefficient surface such as gravel, from 30-50 MPH while using snapshot feature set to trip on any ABS DTC. If fault still does not repeat, use Tech 1 enhanced diagnostic information to determine if fault should be diagnosed further. Enhanced diagnostic information is under DTC HISTORY.
After all system faults have been corrected, clear ABS DTCs. See CLEARING CODES