GM Service Manual Online
For 1990-2009 cars only

Step

Action

Yes

No

Schematic Reference: Exterior Lights Schematics

1

Did you perform the Lighting Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - Lighting Systems

2

Observe the stop lamps while pressing the brake pedal.

Does the system operate normally?

Go to Testing for Electrical Intermittents in Wiring Systems

Go to Step 3

3

Are all the stop lamps inoperative?

Go to Step 8

Go to Step 4

4

Is the CHMSL the only inoperative lamp?

Go to Step 10

Go to Step 5

5

Are both rear stop lamps inoperative while the CHMSL operates correctly?

Go to Step 12

Go to Step 6

6

Test the CHMSL supply voltage circuit of the inoperative lamp for high resistance, an open, or 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 7

7

Test the ground circuit of the inoperative lamp for high resistance or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 21

Go to Step 14

8

Test the battery positive circuit of the stop lamp switch for high resistance, an open or 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 9

9

Test the stop lamp signal circuit of the stop lamp switch 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 16

10

Test the trailer CHMSL supply voltage circuit for high resistance, an open, or 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 11

11

Test the ground circuit of the CHMSL for high resistance or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 21

Go to Step 15

12

Test the CHMSL supply voltage circuit of the CHMSL for high resistance, an open, or 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 13

13

  1. Disconnect an inoperative lamp.
  2. Apply the brake pedal.
  3. Connect a test lamp between the CHMSL supply voltage circuit of the inoperative lamp and good ground.

Does the test lamp illuminate?

Go to Step 14

Go to Step 17

14

Inspect for poor connections at the harness connector of the bulb. 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 21

Go to Step 18

15

Inspect for poor connections at the harness connector of the high mount. 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 21

Go to Step 19

16

Inspect for poor connections at the harness connector of the 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 21

Go to Step 20

17

Repair the open in the ground circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 21

--

18

Replace the rear stop lamp. Refer to Tail/Turn Signal Lamp Replacement .

Did you complete the replacement?

Go to Step 21

--

19

Replace the high mounted stop lamp. Refer to High Mount Stop Lamp Replacement .

Did you complete the replacement?

Go to Step 21

--

20

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

Did you complete the replacement?

Go to Step 21

--

21

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 3