GM Service Manual Online
For 1990-2009 cars only

Diagnostic Aids

Important: The stop lamps will not illuminate unless the ignition is in the ON position. For more detailed information concerning stop lamp operation, refer to Exterior Lighting Systems Description and Operation .

Thoroughly inspect the wiring and connectors. An incomplete inspection of the wiring and connectors may result in misdiagnosis causing part replacement with the reappearance of the malfunction. If an intermittent malfunction exists, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Step

Action

Yes

No

Schematic Reference: Exterior Lights Schematics

Connector End View Reference: Master Electrical Component List in Wiring Systems

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

  1. Turn ON the ignition, with the engine OFF.
  2. Depress and hold the brake pedal.
  3. Observe the high mounted stop lamp (HMSL).
  4. Release the brake pedal.

Did the HMSL operate properly?

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 3

3

Are DTCs P0719 or P0724 set as current?

Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

Go to Step 4

4

  1. Turn OFF the ignition.
  2. Disconnect the stop lamp relay. Refer to Relay Replacement in Wiring Systems.
  3. Connect a test lamp between the stop lamp relay control side supply voltage circuit and the stop lamp relay control circuit.
  4. Turn ON the ignition, with the engine OFF.
  5. Depress and hold the brake pedal.

Does the test lamp illuminate?

Go to Step 5

Go to Step 11

5

  1. Turn ON the ignition, with the engine OFF.
  2. Probe the stop lamp relay switch side supply voltage circuit with a test lamp that is connected to ground.

Does the test lamp illuminate?

Go to Step 6

Go to Step 12

6

  1. Turn OFF the ignition.
  2. Connect a 15-amp fused jumper between the stop lamp relay switch side supply voltage circuit and the HMSL supply voltage circuit.
  3. Turn ON the ignition, with the engine OFF.

Does the HMSL illuminate?

Go to Step 10

Go to Step 7

7

  1. Turn OFF the ignition.
  2. Install the stop lamp relay.
  3. Disconnect the HMSL. Refer to Tail Lamp, Turn Signal Lamp, High Mount Stop Lamp, License Lamp, Backup Lamp Replacement - Rear .
  4. Connect a test lamp between the HMSL supply voltage circuit and the HMSL ground circuit.
  5. Turn ON the ignition, with the engine OFF.
  6. Depress and hold the brake pedal.

Does the test lamp illuminate?

Go to Step 9

Go to Step 8

8

Test the HMSL supply voltage circuit for an open or high resistance or short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 17

Go to Step 13

9

Inspect for poor connections at the HMSL harness connector. 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 17

Go to Step 15

10

Inspect for poor connections at the stop 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 17

Go to Step 14

11

Inspect for poor connections at the harness connector of the body control module (BCM). 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 17

Go to Step 16

12

Locate and repair an open or high resistance in the stop lamp relay switch side supply voltage circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 17

--

13

Locate and repair an open or high resistance in the HMSL ground circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 17

--

14

Replace the stop lamp relay. Refer to Relay Replacement in Wiring Systems.

Did you complete the replacement?

Go to Step 17

--

15

Replace the HMSL. Refer to Tail Lamp, Turn Signal Lamp, High Mount Stop Lamp, License Lamp, Backup Lamp Replacement - Rear .

Did you complete the replacement?

Go to Step 17

--

16

Replace the BCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 17

--

17

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 2