For 1990-2009 cars

Step | Action | Yes | No
--- | --- | --- | ---
Schematic Reference: Exterior Lights Schematics . Connector End View Reference: Component Connector End Views .
1 | Did you perform the Lighting Systems Diagnostic System Check? | Go to Step 2 | Go to Diagnostic System Check - Vehicle .
2 | Place the headlamp switch in the Low Beam position. Do the low beam headlamps operate normally? | Go to Testing for Intermittent Conditions and Poor Connections . | 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 . Did you find and correct the condition? | System OK | Go to Step 9
5 |

1. Place the headlamp switch in the HEAD position.
2. Place the headlamp dimmer switch in the low beam position.
3. With a scan tool, monitor the Low Beam Relay Command data parameter in the body control module (BCM) data list.

Does the scan tool display On?

Replace the underhood fuse block. Refer to Underhood Electrical Center or Junction Block Replacement .

Go to Step 6

6 | Disconnect the turn signal switch. Do the low beam headlamps illuminate? | Go to Step 7 | Go to Step 11
7 | Test the headlamp dimmer switch signal circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs . Did you find and correct a condition? | System OK | 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 . Did you find and correct a condition? | System OK | Go to Step 10
9 | Inspect for poor connections at the harness connector of the inoperative bulb. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | System OK | Replace the inoperative bulb. Refer to Headlamp Bulb Replacement .
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? | System OK | Replace the headlamp dimmer switch. Refer to Turn Signal Switch Replacement .
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? | System OK | Replace the BCM. Refer to Control Module References , for replacement, setup, and programming.