Diagnostic System Check - ABS

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SYSTEM DESCRIPTION
The diagnostic system check is an organized method of identifying any problems caused by a malfunction in either of the following systems:
^ The Antilock Brake System (ABS)
^ The Enhanced Traction Control System (ETS)
^ The Traction Control System (TCS)

The service technician must begin diagnosis of any ABS or ABS/TCS complaint with the diagnostic system check.

The diagnostic system check directs the service technician to the next logical step in diagnosing the complaint.

The EBCM/EBTCM exchanges serial data through the connector C1 terminal A.

Connector C1 terminal AS supplies the switched ignition voltage to the EBCM/EBTCM.

Connector C1 terminal B12 supplies the battery voltage to the EBCM/EBTCM.

Connector C2 terminal C supplies the switched battery voltage to the EBCM/EBTCM.

Connector C2 Terminal D provides the ground for the EBCM/EBTCM.

DIAGNOSTIC PROCESS
Use the following ordered procedure when servicing the ABS/ETS/TCS.

Failure to use the following procedure may cause the loss of important diagnostic data

IMPORTANT diagnostic data. Failure to use the following procedure may lead to difficult and time-consuming diagnosis procedures.

1. Use the following procedure to perform a vehicle preliminary diagnosis inspection:
^ Inspect the brake master cylinder fluid reservoir:
- Verify that the brake fluid level is correct.
- Inspect the master cylinder for contamination.

^ Inspect the brake modulator for the following conditions:
- Leaks
- Wiring damage

^ Inspect the brake components of all four wheels:
- Verify that no drag exists.
- Verify that the brake apply operation is correct.

^ Inspect for worn or damaged wheel bearings. Worn or damaged wheel bearings may cause a wheel to "wobble".
^ Inspect the wheel speed sensors and the wheel speed sensor wirings:
- Verify that all of the sensors solidly attach.
- Inspect for wiring damage, especially at vehicle attachment points.

^ Inspect the outer CV joint:
- Verify that the outer CV joint is aligned correctly.
- Verify that the outer CV joint operates correctly.

^ Inspect the tires. Verify that the tires meet legal trend depth requirements.

2. Perform the Diagnostic System Check. If any DTCs are displayed, select Diagnostic Trouble Code (DTC) History.
2.1. Determine which malfunction occurred the most recently.
2.2. Diagnose and repair the most recent malfunction first.

3. Determine if the following conditions exist: No DTCs are present.
^ There are malfunctions in the mechanical components.
^ The failure is intermittent and cannot be reproduced.

4. If the above conditions exist, attempt to reproduce the malfunction:
4.1. Use the automatic snapshot feature of the Scan Tool while test driving the vehicle. Perform normal acceleration, stopping, and turning maneuvers during the test drive.
4.2. If the test drive does not reproduce the malfunction, perform an ABS stop:
- Perform the stop on a low coefficient surface (such as gravel).
- Perform the stop from a speed of 48-80 km/h (30-50 mph).
- Trigger the snapshot mode on any ABS/ETS/TCS DTC while performing the stop.

4.3. If the ABS stop does not reproduce the malfunction, use the enhanced diagnostic information in the DTC History in order to determine if further diagnosis is needed. This determination will be based on the frequency of failure.

5. Clear the ABS/ETS/TCS DTCs after all of the system malfunctions have been corrected.

DIAGNOSTIC AIDS
Communication with the EBCM/EBTCM is not possible when excessive resistance exists in the following components:
^ The ground
^ The power supply circuits

If communication with the EBCM/EBTCM is not possible, perform the following actions:
^ Verify that the EBCM/EBTCM ground connection is good.
^ Verify that no excessive resistance exists in any of the power supply circuits.

IMPORTANT: Zero the J 39200 test leads before making any resistance measurements. Refer to the J 39200 user's manual.