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

  1. Place the headlamp switch in the ON position.
  2. Place the dimmer switch in the low beam position.

Do the low beam headlamps operate normally?

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

Go to Step 3

3

Is only one low beam headlamp inoperative?

Go to Step 4

Go to Step 5

4

Test the headlamp low beam supply voltage and ground circuits 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 20

Go to Step 12

5

  1. Disconnect the headlamp low relay.
  2. Connect a test lamp between the control circuit of the headlamp low relay and the battery positive voltage circuit of the headlamp low relay connector.

Does the test lamp illuminate?

Go to Step 17

Go to Step 6

6

  1. Connect the headlamp low relay.
  2. Place the headlamp switch in the HEAD position.
  3. Disconnect the multifunction switch.

Do the low beam headlamps illuminate?

Go to Step 13

Go to Step 7

7

Test the headlamp dimmer switch signal circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct a condition?

Go to Step 20

Go to Step 8

8

Test the headlamp switch flash to pass signal circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct a condition?

Go to Step 20

Go to Step 9

9

Test for a short to battery positive voltage or an open in the headlamp low beam relay control circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct a condition?

Go to Step 20

Go to Step 10

10

  1. Disconnect the headlamp switch.
  2. Install a jumper between ground and headlamp switch headlamps on signal circuit.
  3. Turn the ignition to the ON position.

Do the headlamps illuminate?

Go to Step 19

Go to Step 11

11

Test for a short to battery positive voltage or an open on the headlamps ON signal circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 20

Go to Step 14

12

Inspect for poor connections at the harness connector of the inoperative blub. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 20

Go to Step 15

13

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 20

Go to Step 18

14

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 20

Go to Step 16

15

Replace the inoperative bulb. Refer to Headlamp Bulb Replacement or Sealed Beam Headlamp Replacement .

Did you complete the replacement?

Go to Step 20

--

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 20

--

17

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

Did you complete the replacement?

Go to Step 20

--

18

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 20

--

19

Replace the headlamp switch. Refer to Headlamp Switch Replacement .

Go to Step 20

--

20

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 3