GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2004 🢒 TopKick C-Series (Conventional) C4/C5 🢒 Brakes 🢒 Air Antilock Brake System 🢒 Status Lamps Illuminated - TRC and MOD

Circuit Description

The EBCM activates the traction control (TC) modulator valve by supplying 12 volts to the TC modulator valve high reference circuit and supplying ground to the TC modulator valve low reference circuit. When the TC modulator valve is energized, an internal valve opens and air pressure is applied to the drive axle BPMVs.

Conditions for Running the Diagnostic Fault
    • The ignition is ON.
    • The EBCM is calibrated for traction control.

Conditions for Setting the Diagnostic Fault

The EBCM detects an open or shorted TC modulator or circuitry.

Action Taken When the Diagnostic Fault Sets
    • The TC system is disabled.
    • The traction off indicator on turns ON.
    • Driver is unable to re-enable the TC system.

Conditions for Clearing the Diagnostic Fault
    • Repair the condition responsible for illuminating the status lamps.
    • Perform the Status Lamps Reset Procedure.

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

Step

Action

Value(s)

Yes

No

Schematic Reference: Air Antilock Brake System Schematics

Connector End View Reference: Air Brake System Component Views

1

Did you perform the ABS Diagnostic System Check?

--

Go to Step 2

Go to Diagnostic System Check - Air ABS

2
  1. Turn the ignition ON.
  2. Observe the LEDs on the EBCM after the ignition has been ON for 10 seconds.

Do the LEDs on the EBCM indicate a current traction control modulator fault?

--

Go to Step 3

Go to Diagnostic Aids

3
  1. Disconnect from the EBCM, the harness connector or connectors containing the TC modulator high and low control circuits.
  2. Use a DMM in order to measure the resistance between the high and low control circuits.

Does the resistance measure within the specified range?

0.5-12 ohms

Go to Step 7

Go to Step 4

4
  1. Disconnect the TC modulator valve harness connector. Refer to Rear Air Brake Relay Valve Replacement .
  2. Test the modulator valve circuits between the modulator valve harness connector and the EBCM harness connector. Test each for the following:
    3. • An open
    • A short to ground
    • A short to voltage
    • Shorted together

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 9

Go to Step 5

5

Inspect for poor connections at the harness connector of the TC modulator valve. 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 9

Go to Step 6

6

Replace the TC modulator valve. Refer to Rear Air Brake Relay Valve Replacement

Did you complete the replacement?

--

Go to Step 9

--

7

Inspect for poor connections at the harness connector for 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 9

Go to Step 8

8

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 9

--

9

Operate the vehicle within the Conditions for Running the Diagnostic Fault.

Do the same red LEDs illuminate?

--

Go to Step 3

Go to Step 10

10

Do any red LEDs illuminate?

--

Go to Diagnostic System Check - ABS

System OK