GM Service Manual Online
For 1990-2009 cars only

Headlamp Low or High Beams Always On Standard

Step

Action

Yes

No

Schematic Reference: Headlights/Daytime Running Lights (DRL) Schematics

Connector End View Reference: Lighting Systems Connector End Views or Data Communication Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

Verify that the high or low beam headlamps are always ON.

Do the high and low beam headlamps operate normally?

Go to Testing for Intermittent Conditions and Poor Connections

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 always 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 Wiring Repairs .

    • 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 always 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 .

Is a ground control signal present?

Go to Step 11

Go to Step 15

8

Remove the headlamp driver module (HDM).

Do the low beam headlamps remain always ON?

Go to Step 13

Go to Step 9

9

Test for a voltage signal at the headlamp low beam relay control circuit connector terminal. Refer to Circuit Testing .

Is a voltage control 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 .

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 .

Did you find and correct the condition?

Go to Step 18

Go to Step 14

12

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

Did you find and correct a condition?

Go to Step 18

--

13

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

Did you find and correct a condition?

Go to Step 18

--

14

Replace the BCM. Refer to Control Module References 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 .

Did you complete the repair?

Go to Step 18

--

16

Replace the HDM. Refer to Relay Replacement .

Did you complete the repair?

Go to Step 18

--

17

Replace the headlamp dimmer switch. Refer to Turn Signal Multifunction Switch Replacement .

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