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 Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle .
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 . | 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 Wiring Repairs .

• | The headlamp dimmer switch signal

• | The headlamp switch flash to pass signal

Did you find and correct a condition?

System OK

Go to Step 6

6 | Remove the LT HI BEAM and RT HIGH BEAM fuses from the underhood body electrical centre (UBEC). Do the high beam headlamps remain ON? | Repair the short to voltage in the right or left high beam headlamp supply voltage circuit. Refer to Wiring Repairs . | Go to Step 7
7 | With a scan tool, monitor the High Beam Relay Command data parameter in the body control module (BCM) data list. Does the scan tool display On? | Go to Step 11 | Replace the UBEC. Refer to Underhood Electrical Center or Junction Block Replacement .
8 | Remove the LT LO BEAM and RT LO BEAM fuses from the UBEC. Do the low beam headlamps remain always ON? | Repair the short to voltage in the right or left low beam headlamp supply voltage circuit. Refer to Wiring Repairs . | Go to Step 9
9 | 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? | Go to Step 11 | Replace the UBEC. Refer to Underhood Electrical Center or Junction Block 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.