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Home >> GMC >> 2002 >> C3500 HD 6.5 F, Standard >> Repair and Diagnosis >> Brakes >> Mechanical - Hydraulic >> Hydraulic Brakes >> Diagnostic Information and Procedures >> Brake Warning Indicator Always On (W/DRLs) >> Test Description

Test Description

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

  1. 4:  Ground is applied to the ABS pressure differential sensor signal circuit if the scan tool displays On.
  2. 5:  This step tests for a shorted brake pressure differential switch.
  3. 6:  This step tests if the EBCM is applying ground to the brake warning indicator.
  4. 8:  This step tests for a shorted park brake warning lamp switch.
  5. 11:  The harness connector of the DRL control module contains 2 separate park brake switch signal circuits.
  6. 14:  This step tests the brake warning indicator control circuit for a short to ground by substituting the IPC and the brake warning indicator lamp with a test lamp.
Brake Warning Indicator Always On (W/DRLs)

Step Action Yes No
Schematic Reference:  Brake Warning System Schematics  
1 Did you review the Brake Warning System Description and Operation and perform the necessary inspections? Go to Step 2  Go to Symptoms - Hydraulic Brakes 
2
  1. Turn OFF the ignition.
  2. Ensure the park brake is released.
  3. Turn ON the ignition while observing the brake warning indicator.
Does the brake warning indicator illuminate for 3 seconds and then turn OFF?		 Go to TESTING FOR INTERMITTENT AND POOR CONNECTIONS in Wiring Systems Go to Step 3 
3
  1. Install a scan tool.
  2. Select the 4WAL 3 Sensor Current Diagnostic Trouble Codes function on the scan tool.
Does the scan tool display DTC C0286 AND any other ABS disabling DTC?		 Go to DIAGNOSTIC TROUBLE CODE (DTC) IDENTIFICATION in Antilock Brake System Go to Step 4 
4 
  1. Select the 4WAL 3 Sensor Data Display function on the scan tool.
  2. Observe the Brake Warning Lamp Command.
Does the scan tool display On?		 Go to Step 5  Go to Step 8 
5  Disconnect the brake pressure differential switch harness connector. Refer to Combination Valve Replacement .
Does the brake warning indicator turn OFF?		 Go to Step 20  Go to Step 6 
6 
  1. Turn OFF the ignition.
  2. Reconnect the brake pressure differential switch harness connector.
  3. Disconnect the 10-way EBCM harness connector. Refer to ELECTRONIC BRAKE CONTROL MODULE (EBCM) REPLACEMENT in Antilock Brake System.
  4. Turn ON the ignition.
Does the brake warning indicator turn OFF?		 Go to Step 16  Go to Step 7 
7 Repair the short to ground in the ABS pressure differential sensor signal circuit. Refer to WIRING REPAIRS in Wiring Systems.
Did you complete the repair?		 Go to Step 21  -
8  Disconnect the park brake warning lamp switch harness connector. Refer to Park Brake Warning Lamp Switch Replacement in Park Brake.
Does the brake warning indicator turn OFF?		 Go to Step 18  Go to Step 9 
9
  1. Turn OFF the ignition.
  2. Remove the DRL control module circuit board. Refer to DAYTIME RUNNING LIGHTS (DRL) CONTROL MODULE REPLACEMENT in Lighting Systems.
  3. Turn ON the ignition.
Does the brake warning indicator turn OFF?		 Go to Step 10  Go to Step 14 
10
  1. Turn OFF the ignition.
  2. Disconnect the ignition switch harness connector. Refer to IGNITION SWITCH REPLACEMENT - ON VEHICLE.
  3. Test the park brake switch signal circuit (ignition switch side) for a short to ground. Refer to CIRCUIT TESTING in Wiring Systems.
Is the park brake switch signal circuit shorted to ground within the ignition switch?		 Go to Step 19  Go to Step 11 
11 
  1. Reconnect the ignition switch harness connector.
  2. Test both of the park brake switch signal circuits 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 21  Go to Step 12 
12 Test the brake warning indicator control circuit for a short to ground between the DRL control module circuit board and the underhood fuse block. Refer to CIRCUIT TESTING and WIRING REPAIRS in Wiring Systems.
Did you find and correct the condition?		 Go to Step 21  Go to Step 13 
13 Replace the DRL control module circuit board. Refer to DAYTIME RUNNING LIGHTS (DRL) CONTROL MODULE REPLACEMENT in Lighting Systems.
Did you complete the replacement?		 Go to Step 21  -
14 
  1. Turn OFF the ignition.
  2. Remove the instrument panel cluster.
  3. Connect a test lamp between the battery positive voltage circuit and the brake warning indicator control circuit at the instrument panel cluster harness connector.
  4. Turn ON the ignition.
Does the test lamp remain illuminated?		 Go to Step 15  Go to Step 17 
15 Repair the short to ground in the brake warning indicator control circuit. Refer to WIRING REPAIRS in Wiring Systems.
Did you complete the repair?		 Go to Step 21  -
16 Replace the EBCM. Refer to ELECTRONIC BRAKE CONTROL MODULE (EBCM) REPLACEMENT in Antilock Brake System.
IMPORTANT: Use the scan tool in order to perform the Tire Size Calibration procedure.

Did you complete the replacement?		 Go to Step 21  -
17 Replace the instrument panel cluster.
Did you complete the replacement?		 Go to Step 21  -
18 Replace the park brake warning lamp switch. Refer to Park Brake Warning Lamp Switch Replacement in Park Brake.
Did you complete the replacement?		 Go to Step 21  -
19 Replace the ignition switch. Refer to IGNITION SWITCH REPLACEMENT - ON VEHICLE.
Did you complete the replacement?		 Go to Step 21  -
20 Replace the brake pressure differential switch. Refer to Combination Valve Replacement .
Did you complete the replacement?		 Go to Step 21  -
21
  1. Turn OFF the ignition for 5 seconds.
  2. Turn ON the ignition while observing the brake warning indicator.
Does the brake warning indicator illuminate for 3 seconds and then turn OFF?		 System OK Go to Step 3 
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