GM Service Manual Online
For 1990-2009 cars only

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

1

Did you perform the Lighting Systems Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - Lighting Systems

2

Verify that the DRL headlamps are inoperative.

Do the DRL headlamps operate normally?

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

Go to Step 3

3

Use the Scan Tool to inspect for the following related Body Control Module (BCM) Data/ Input Parameters and Output Controls.

Refer to Scan Tool Data List for typical values and definitions.

    • Headlamp Ambient Light Sensor
    • Park Brake Switch
    • Auto Headlamps
    • Headlamp Relay Feedback
    • Daytime Running Lamps Relay
    • Headlamp Power Relay
    • High Beam Switch
    • Flash to Pass Switch

Did you find and correct a condition?

Go to Step 10

Go to Step 4

4

Turn the headlamp switch to the HEAD position.

Do the headlamps operate properly in the LO position?

Go to Step 5

Go to Headlamps Inoperative - Low Beams

5

Place the multifunction headlamp dimmer switch in the HI position.

Do the headlamps operate properly in the HI position?

Go to Step 6

Go to Headlamps Inoperative - High Beams

6

Inspect the GAUGES fuse in the IP fuse block.

Is the fuse open?

Go to Step 8

Go to Step 7

7

Test the following circuits and the DRL diode for an open or high resistance. Refer to Circuit Testing in Wiring Systems.

    • Ignition 1 voltage
    • Daytime Running Lamp (DRL) relay control
    • DRL diode signal
    • DRL diode supply voltage

Was a problem found?

Go to Step 9

Go to Step 11

8

Test the ignition 1 voltage circuit for a short to ground. Refer to Circuit Testing in Wiring Systems.

Was a problem found?

Go to Step 10

Go to Step 11

9

Replace the DRL diode as necessary or repair the open or high resistance in one of the following circuits. Refer to Wiring Repairs in Wiring Systems.

    • Ignition 1 voltage
    • Daytime Running Lamp (DRL) relay control
    • DRL diode signal
    • DRL diode supply voltage

Did you complete the repair?

Go to Step 12

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10

Repair the short to ground in the ignition 1 voltage circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 12

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11

Replace the DRL relay.

Did you complete the repair?

Go to Step 12

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12

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 3