Vehicle on-Board Diagnostics

When servicing the ABS system, the following steps should be followed in order. Failure to follow these steps may result in the loss of important diagnostic data and may lead to difficult and time consuming diagnosis procedures:
1. Using the Tech 1 scan tool, read all current and history diagnostic trouble codes. Be certain to note which codes are current malfunctions. DO NOT CLEAR CODES unless directed to do so.
2. Using the Tech 1, read the DTC HISTORY data. Note the DTCs stored and their frequency of failure. Specifically, note the last failure that occurred and the conditions present when this failure occurred. This "last failure" is what brought the customer in for service, and should be the starting point for diagnosis and repair.
3. Perform a vehicle preliminary diagnosis inspection. This should include:
^ Inspection of the master cylinder fluid reservoir for proper brake fluid level and signs of fluid contamination.
^ Inspection of the hydraulic modulator for any leaks or wiring damage.
^ Inspection of brake components at all four (4) wheels. Verify no drag exists. Also, verify proper brake apply operation.
^ Inspection for worn or damaged front wheel bearings that may allow a wheel to "wobble."
^ Inspection of the wheel speed sensors and their wiring. Verify correct air gap range, solid sensor attachment, undamaged sensor toothed ring and undamaged wiring, especially at vehicle attachment points.
^ Verify proper outer CV joint alignment and operation.
^ Verify tires meet legal tread depth requirements.
4. If no DTCs are present, or no mechanical component malfunctions are present, perform the "Modulator Test" using the Tech 1 or T-100 to isolate the cause of the problem. If the failure is intermittent and not reproduceable, test drive the vehicle while using the automatic snapshot feature of the Tech 1.

Perform normal acceleration, stopping, and turning maneuvers. If this does not reproduce the malfunction, perform an ABS stop, on a low coefficient surface such as gravel, from approximately 48-80 km/h (30-50 mph) while triggering the snapshot mode on any ABS DTC. If the failure is still not reproduceable, use the enhanced diagnostic information found in DTC HISTORY to determine whether or not this malfunction should be diagnosed further.
5. Once all system malfunctions have been corrected, clear the ABS DTCs.

SELF-DIAGNOSTICS
The EBCM contains sophisticated on-board diagnostics that, when accessed with a Tech 1 scan tool, are designed to identify the source of any system malfunction as specifically as possible, including whether or not the malfunction is intermittent. There are 57 diagnostic trouble codes to assist with diagnosis.

When using the Tech 1 with ABS VI, the last diagnostic trouble code is specifically identified, and specific ABS data is stored at the time of this malfunction. Also, in addition to the last code set, there is information about the first five codes set. Using the Tech 1, each input and output can be monitored, thus enabling malfunction confirmation and repair verification. Manual control of components and automated functional tests are also available when using the Tech 1.