Diagnostic System Check

Part 1 Of 2:

Part 2 Of 2:

SYSTEM DESCRIPTION
The diagnostic system check is an organized approach to identifying an Antilock Brake System (ABS) malfunction. The diagnostic system check must be the starting point for any ABS complaint diagnosis. The diagnostic system check directs the service technician to the next logical step in diagnosing the complaint.

Diagnostic serial data is transmitted/received by the EBCM through connector C1, terminal F (over 15,000 GVW), or terminal G (under 15,000 GVW). The EBCM is supplied switched ignition voltage through connector C1, terminal A, and ground is provided through connector C1, terminal J.

DIAGNOSTIC AIDS
Excessive resistance in the ground or power supply circuits will not allow communication with the EBCM. If communication with the EBCM is not possible, ensure that the ABS ground connection is good and that there is no excessive resistance in any of the power supply circuits.

TEST DESCRIPTION
The numbers below refer to the steps in the diagnostic table:
3. This step checks for normal ABS indicator lamp operation.
4. This step checks for ignition voltage at the EBCM.
5. This step checks for high resistance in the ground circuit.
9. This step checks for high resistance in the ignition voltage circuit.
10. This step checks for a short to ground in the ignition voltage circuit.
11. This step decides between ABS indicator lamp on always, or off always as the symptom.
15. This step decides between a short to ground in the 10-way EBCM harness/connector, or an internal EBCM fault.