GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2004 🢒 TopKick C-Series (Conventional) C4/C5 🢒 Brakes 🢒 Antilock Brake System 🢒 ABS Indicator Always On

Circuit Description

The instrument panel cluster (IPC) illuminates the antilock brake system (ABS) indicator by supplying ground to the lamp. The electronic brake control module (EBCM) sends class 2 serial data messages to the IPC in order to command the indicator ON or OFF.

Diagnostic Aids

Important: Do not proceed with this document if any DTCs are present, or if the ABS module is not communicating with the scan tool. Follow the diagnostic procedures for the listed DTCs, or for Data Communications. Intermittent symptoms indicate possible problems with wiring, connectors, or grounds. Make sure the EBCM has clean and tight ground contacts. Check for corrosion of crimped terminal connections in EBCM connector. The malfunction must be present during diagnosis in order to prevent unnecessary parts replacement. Always begin diagnosis with the Diagnostic System Check.

Test Description

The number below refers to the step number on the diagnostic table.

  1. This step tests if the IPC is able to turn OFF the ABS indicator.

Step

Action

Yes

No

Important: After a wheel speed sensor DTC is cleared and the ignition is ON, the ABS indicator may remain ON until the EBCM completes a power-up self test. This test concludes when the vehicle reaches a speed greater than 20 km/h (13 mph) and the wheel speeds are verified by the EBCM.

1

Did you perform the ABS Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - ABS

2
  1. Turn OFF the ignition for 5 seconds.
  2. Turn ON the ignition while observing the ABS indicator.

Does the ABS indicator illuminate for 2 seconds and then turn OFF?

Go to Diagnostic Aids

Go to Step 3

3

  1. Select the Instrument Panel Cluster Special Functions menu on the scan tool.
  2. Use the scan tool to command all of the IPC indicators Off.

Does the ABS indicator turn OFF?

Go to Step 5

Go to Step 4

4

Replace the Instrument Panel Cluster. Refer to Instrument Cluster Replacement in Instrument Panel, Gages, and Console.

Did you complete the replacement?

Go to Step 6

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5

Important: Following EBCM replacement, use the scan tool to perform the Tire Size/Wheel Base Calibration procedure.

Replace the EBCM. Refer to Electronic Brake Control Module Replacement .

Did you complete the replacement?

Go to Step 6

--

6
  1. Turn OFF the ignition for 5 seconds.
  2. Turn ON the ignition while observing the ABS indicator.

Does the ABS indicator illuminate for 2 seconds and then turn OFF?

System OK

Go to Step 3