GM Service Manual Online
For 1990-2009 cars only

Step

Action

Yes

No

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

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

1

Did you perform the Lighting Systems Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - Lighting Systems

2

  1. Turn ON the ignition, with the engine OFF.
  2. Turn OFF the twilight switch.
  3. Turn ON the headlamps.
  4. Turn ON and OFF the headlamp high beam switch.
  5. Turn OFF the headlamps.
  6. Turn OFF the ignition.

Do the headlamps operate properly?

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

Go to Step 3

3

Are the low beam headlamps always ON?

Go to Step 4

Go to Step 7

4

Disconnect the headlamp switch.

Did the headlamps turn OFF?

Go to Step 15

Go to Step 5

5

Test the headlamp switch headlamps on signal circuit 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 6

6

Disconnect the lamp control module (LCM).

Did the headlamps turn OFF?

Go to Step 11

Go to Step 17

7

Disconnect the headlamp dimmer switch.

Did the headlamps turn OFF?

Go to Step 13

Go to Step 8

8

Test the headlamp switch flash to pass signal circuit of the headlamp dimmer 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 9

9

Test the headlamp dimmer switch high beam signal circuit of the LCM 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 10

10

Disconnect the LCM.

Did the headlamps turn OFF?

Go to Step 11

Go to Step 16

11

Test the ignition 1 voltage circuit of the LCM for a short to voltage. 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 headlamp alarm signal circuit of the LCM 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 14

13

Inspect for poor connections at the harness connector of the headlamp dimmer 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 18

14

Inspect for poor connections at the harness connector of the LCM. 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

15

Inspect for poor connections at the harness connector of the headlamp 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

16

Repair short to battery positive voltage in the headlamp high beam supply voltage circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 21

--

17

Repair short to battery positive voltage in the headlamp low beam supply voltage circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 21

--

18

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

Did you complete the replacement?

Go to Step 21

--

19

Replace the LCM. Refer to Lamp Control Module Replacement .

Did you complete the replacement?

Go to Step 21

--

20

Replace the headlamp switch. Refer to Headlamp Switch Replacement .

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 2