Initial Inspection and Diagnostic Overview

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

Serial data is transmitted by the EBCM through terminal "2." The EBCM is supplied switched ignition voltage through terminal "14," battery voltage through terminal "15" and switched battery voltage through terminal "A." The EBCM ground is provided through terminal "B."

Diagnostic System Check (1 Of 4):

Diagnostic System Check (2 Of 4):

Diagnostic System Check (3 Of 4):

Diagnostic System Check (4 Of 4):

Diagnostic System Check:

Chart Test Description
Number(s) below refer to circled number(s) on the diagnostic chart.
1. Indicates if EBCM is transmitting data.
2. Checks for a serial data link malfunction.
3. Checks for proper Tech 1 connection to DLC.
4. Checks for open HVAC fuse.
5. Checks for open CLSTR fuse.
6. Checks for high resistance in the EBCM battery feed circuit.
7. Checks for current DTC's.
8. Checks for proper "ABS" warning lamp operation.
9. Checks for history DTC's.
10. Checks for possible short to ground in the switched ignition circuitry.
11. Isolates the short to ground to either the circuitry or the EBCM.
12. Ensures short to ground is not due to physical damage of the circuitry.
13. Checks for possible short to ground in the battery feed circuitry.
14. Isolates the short to ground to either the circuitry or the EBCM.
15. Ensures short to ground is not due to physical damage of the circuitry.
16. Checks for proper battery feed voltage at the EBCM.
17. Checks for proper ignition feed voltage at the EBCM.
18. Checks for high resistance in the battery feed circuit and the switched ignition feed circuit.
19. Ensures malfunction is not due to poor terminal contact.
20. Checks for an open circuit in the battery feed circuit between the fuse block and the EBCM.
21. Checks for an open circuit in the switched ignition feed circuit between the fuse block and the EBCM.
22. Isolates the high resistance circuit to either the battery feed circuit or the switched ignition feed circuit.
23. Isolates the high resistance in the battery feed circuit between the fuse block and the EBCM.
24. Isolates the high resistance in the ignition feed circuit between the fuse block and the EBCM.

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 the ABS ground connection is good and that there is no excessive resistance in any of the power supply circuits.