GM Service Manual Online
For 1990-2009 cars only

Step

Action

Yes

No

Schematic Reference: Headlights Schematics

Connector End View Reference: Lighting Systems Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

Place the headlamp switch in the OFF position.

Do the high and low beam headlamps operate normally?

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

Go to Step 3

3

Are only the high beam headlamps always ON?

Go to Step 4

Go to Step 8

4

Disconnect the headlamp dimmer switch.

Do the high beam headlamps remain ON?

Go to Step 5

Go to Step 10

5

Test the following circuits for a short to ground as applicable. Refer to Circuit Testing and Circuit Testing in Wiring Systems.

    • The headlamp dimmer switch signal
    • The headlamp switch flash to pass (FTP) signal

Did you find and correct a condition?

Go to Step 18

Go to Step 6

6

Remove the high beam relay.

Do the high beam headlamps remain ON?

Go to Step 12

Go to Step 7

7

Test for a ground signal at the high beam relay control circuit connector terminal. Refer to Circuit Testing in Wiring Systems.

Is a ground control signal present?

Go to Step 11

Go to Step 15

8

Remove the low beam relay.

Do the low beam headlamps remain always ON?

Go to Step 13

Go to Step 9

9

Test for a ground signal at the headlamp low beam relay control circuit connector terminal. Refer to Circuit Testing in Wiring Systems.

Is a ground signal present?

Go to Step 11

Go to Step 16

10

Inspect for poor connections at the harness connector of the headlamp dimmer switch. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 18

Go to Step 17

11

Inspect for poor connections at the harness connector of the body control module (BCM). Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 18

Go to Step 14

12

Repair the short to battery positive voltage in the right or left high beam headlamp supply voltage circuit. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct a condition?

Go to Step 18

--

13

Repair the short to battery positive voltage in the right or left low beam headlamp supply voltage circuit. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct a condition?

Go to Step 18

--

14

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 18

--

15

Replace the high beam headlamp relay. Refer to Relay Replacement in Wiring Systems.

Did you complete the repair?

Go to Step 18

--

16

Replace the low beam relay. Refer to Relay Replacement in Wiring Systems.

Did you complete the repair?

Go to Step 18

--

17

Replace the headlamp dimmer switch. Refer to Turn Signal Multifunction Switch Replacement in Steering Wheel and Column.

Did you complete the repair?

Go to Step 18

--

18

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 3