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

Circuit Description

The EBCM receives a signal from the trailer ABS module over the ignition 1 voltage circuit. The EBCM applies ground to the trailer ABS indicator control circuit in order to turn ON the TRAILER ABS indicator.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step tests if the trailer is the cause of the indicator staying on. If the vehicle does not have a trailer go to step 3.

Step

Action

Yes

No

Schematic Reference: Air Antilock Brake System Schematics

1

Did you perform the Air ABS Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - Air ABS

2

Disconnect the trailer from the vehicle.

Does the TRAILER ABS indicator turn OFF?

The problem is with the trailer. Refer to the trailer manufacturer.

Go to Step 3

3

Disconnect the EBCM.

Does the TRAILER ABS Indicator turn OFF?

Go to Step 6

Go to Step 4

4
  1. Disconnect from the Telltale Circuit Board, the harness connector containing the trailer ABS indicator control circuit.
  2. Test the trailer ABS indicator control circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems

Did you find and correct the condition?

Go to Step 7

Go to Step 5

5

Replace the Telltale Circuit Board. Refer to Telltale Circuit Board Replacement in Instrument Panel, Gages and Console.

Did you complete the repair?

Go to Step 7

--

6

Important: Following EBCM replacement, perform the EBCM self-configuration procedure.

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

Did you complete the replacement?

Go to Step 7

--

7
  1. Turn OFF the ignition for 5 seconds.
  2. Turn ON the ignition while observing the TRAILER ABS Indicator.

Does the TRAILER ABS Indicator turn ON?

Go to Step 2

System OK