GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 GMC C-Series Medium Duty Truck B7 🢒 DTC 🢒 DTC C0281 or C081

Circuit Description

The brake switch signal informs the EBCM when the brake is applied. The EBCM sends a 12 volt signal to the stoplamp switch via the brake switch signal circuit. The stoplamp switch grounds the circuit when the brake is released and opens the circuit when the brake is applied. Feedback to the EBCM is low when the brake is released.

Conditions for Running the DTC

Either of the following conditions will cause the DTC to run:

    • The ignition is ON and the vehicle achieves at least 56 km/h (35 mph) before coming to a stop.
    • The ignition is ON and the vehicle experiences an antilock brake system (ABS) event lasting at least 1 second.

Conditions for Setting the DTC

The EBCM detects an open or shorted brake switch or brake switch circuit.

Action Taken When the DTC Sets
    • The EBCM disables the ABS.
    • The ABS indicator turns ON.

Conditions for Clearing the DTC

The conditions for setting the DTC are no longer present and you use the scan tool Clear DTCs function.

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 tests for a shorted stop lamp switch.

    2.

  2. This step tests for an open stop lamp switch.

Step

Action

Yes

No

Schematic Reference: Antilock Brake System Schematics

1

Did you perform the ABS Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - ABS

2
  1. Install a scan tool.
  2. Select the Hydraulic 4WAL 4 Sensor Data Display function.
  3. Observe the Brake Switch Status on the scan tool.

Does the scan tool display Off?

Go to Step 3

Go to Step 5

3
  1. Apply the brake.
  2. Observe the Brake Switch Status on the scan tool.

Does the scan tool display On?

Go to Diagnostic Aids

Go to Step 4

4

  1. Turn OFF the ignition.
  2. Disconnect the stop lamp switch harness connector. Refer to Stop Lamp Switch Replacement in Hydraulic Brakes.
  3. Turn ON the ignition.
  4. Observe the Brake Switch Status on the scan tool.

Does the scan tool display On?

Go to Step 9

Go to Step 7

5

  1. Turn OFF the ignition.
  2. Disconnect the stop lamp switch harness connector. Refer to Stop Lamp Switch Replacement in Hydraulic Brakes.
  3. Connect a fused jumper wire between the ground circuit and the brake switch signal circuit at the stop lamp switch harness connector. Refer to Using Fused Jumper Wires in Wiring Systems.
  4. Turn ON the ignition.
  5. Observe the Brake Switch Status on the scan tool.

Does the scan tool display Off?

Go to Step 9

Go to Step 6

6

Test the ground circuit and the brake switch signal circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 12

Go to Step 8

7

Test the brake switch signal 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 12

Go to Step 8

8

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 12

Go to Step 10

9

Inspect for poor connections at the harness connector of the stop lamp switch. 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 12

Go to Step 11

10

Important: Following EBCM replacement, use the scan tool to perform the Tire Size Calibration procedure and the Trim Level Calibration procedure.

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

Did you complete the replacement?

Go to Step 12

--

11

Replace the stop lamp switch. Refer to Stop Lamp Switch Replacement in Hydraulic Brakes.

Did you complete the replacement?

Go to Step 12

--

12
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

Go to Step 2

System OK