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 Inoperative

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 for an open in the trailer ABS indicator control circuit. If the fuse in the jumper wire opens while performing this test, the circuit is shorted to voltage.

    2.

  2. This step tests the circuit the trailer ABS module uses to send the frequency signal back to the EBCM.

    3.

  3. This step identifies devices that may cause interference with the frequency sent from the trailer ABS module.

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

  1. Disconnect the EBCM connector containing the trailer ABS indicator control circuit.
  2. Using a fused jumper wire, connect the trailer ABS indicator control circuit to a good ground.
  3. Turn ON the ignition.

Does the TRAILER ABS indicator turn ON?

Go to Step 8

Go to Step 3

3
  1. Turn OFF the ignition.
  2. Remove the Telltale Circuit Board.
  3. Connect a test lamp between the ignition 1 voltage circuit and a good ground.
  4. Turn ON the ignition.

Does the test lamp illuminate?

Go to Step 5

Go to Step 4

4

Repair the open in the ignition 1 voltage circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 13

--

5

Test the trailer ABS indicator control circuit for an open or short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 6

6

Inspect the TRAILER ABS indicator bulb for an open or burned out filament.

Did you find and correct the condition?

Go to Step 13

Go to Step 7

7

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

Did you complete the replacement?

Go to Step 13

--

8

Test the ignition 1 voltage circuit for an open between the EBCM and the trailer wiring harness connector. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 9

9

Verify that the trailer is equipped with ABS and is functioning properly.

Does the trailer operate properly?

Go to Step 10

Go to Step 12

10

Inspect for devices that may cause interference with the ABS signal from the trailer. Refer to Checking Aftermarket Accessories

Did you find and correct the condition?

Go to Step 13

Go to Step 11

11

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 13

--

12

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

Did you complete the repair?

Go to Step 13

--

13

Verify the repair.

Does the system operate normally?

System OK

Go to Step 2