GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 GMC C-Series Medium Duty Truck B7 🢒 Brakes 🢒 Air Antilock Brake System 🢒 Air ABS Indicator Inoperative

Circuit Description

The EBCM applies ground to the brake lamp relay control circuit in order to energize the ABS indicator lamp relay and turn OFF the ABS indicator.

Diagnostic Aids

Thoroughly inspect connections or circuitry that may cause an intermittent malfunction. Refer to the following:

    •  Testing for Electrical Intermittents
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs
    •  Connector Repairs

Test Description

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

  1. This step simulates the EBCM commanding the ABS indicator ON.

    2.

  2. This step tests for stuck open ABS indicator lamp relay contacts.

    3.

  3. This step tests the ABS indicator failure control circuit for an open by substituting the Instrument Panel Cluster (IPC) and the ABS indicator lamp with a test lamp.

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

Does the ABS indicator turn ON for approximately 7 seconds, turn OFF, blink ON and OFF twice and then remain OFF?

Go to Diagnostic Aids

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect from the EBCM, the harness connector containing the brake lamp relay control circuit.

Does the ABS indicator turn ON?

Go to Step 10

Go to Step 4

4

  1. Disconnect the ABS indicator lamp relay.
  2. Use a fused jumper wire in order to connect the ABS indicator failure control circuit to the ground circuit of the ABS indicator lamp relay.

Does the ABS indicator turn ON?

Go to Step 8

Go to Step 5

5

Test the ground circuit of the ABS indicator lamp relay for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 15

Go to Step 6

6

  1. Turn OFF the ignition.
  2. Reconnect the ABS indicator lamp relay.
  3. Disconnect from the instrument panel cluster, the harness connector containing the ABS failure control circuit. Refer to Instrument Cluster Replacement in Instrument Panel, Gages , and Console.
  4. Connect a test lamp between the battery positive voltage circuit and the ABS indicator failure control circuit.
  5. Turn ON the ignition.

Does the test lamp illuminate?

Go to Step 7

Go to Step 14

7

Inspect the ABS lamp for an open filament.

Did you find and correct the condition?

Go to Step 15

Go to Step 11

8

Inspect for poor connections at the harness connector of the ABS indicator lamp relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 15

Go to Step 9

9

Replace the ABS indicator lamp relay.

Did you complete the replacement?

Go to Step 15

--

10

Inspect for poor connections at the harness connector of the EBCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 15

Go to Step 13

11

Inspect for poor connections at the harness connector of the IPC. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 15

Go to Step 12

12

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

Did you complete the replacement?

Go to Step 15

--

13

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 15

--

14

Repair the open in the ABS indicator failure control circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 15

--

15
  1. Turn OFF the ignition for 5 seconds.
  2. Turn ON the ignition while observing the ABS indicator.

Does the ABS indicator turn ON for approximately 7 seconds, turn OFF, blink ON and OFF twice and then remain OFF?

System OK

Go to Step 3