GM Service Manual Online
For 1990-2009 cars only

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

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

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

Turn ON the headlamps.

Do both low beam headlamps illuminate?

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 8

Go to Step 4

4

Are the park lamps ON?

Go to Step 5

Go to Step 6

5

  1. Remove the low beam relay.
  2. Connect a test lamp between the low beam relay control circuit and battery positive voltage.

Does the test lamp illuminate as expected?

Go to Step 11

Go to Step 13

6

Using a scan tool, observe the Low Beam Switch Input parameter.

Does the parameter indicate ON?

Go to Step 12

Go to Step 7

7

Test the headlamp switch headlamps ON signal, and the ground circuit of the headlamp switch for the following:

    • An open
    • A high resistance
    • A short to voltage

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 18

Go to Step 10

8

Test the low beam headlamp voltage supply and ground circuits of the inoperative headlamp for the following:

    • An open
    • A high resistance
    • A short to ground

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 18

Go to Step 9

9

Inspect for a poor connections at the harness connector of the inoperative headlamp. 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 18

Go to Step 14

10

Inspect for a 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 18

Go to Step 15

11

Inspect for a poor connections at the harness connector of the low beam relay. 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 18

Go to Step 16

12

Inspect for a poor connections at the harness connector of the body control module (BCM). 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 18

Go to Step 17

13

Important: The BCM may need to be reset if a short to voltage is repaired. To reset the BCM, remove the STOP/TURN and the CHMSL/BACKUP fuses in the instrument panel (I/P) fuse panel for 10 seconds. with the ignition key in the OFF position.

Repair the low beam relay control circuit of the BCM for the following:

    • An open
    • A high resistance
    • A short to voltage

Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 18

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14

Replace the inoperative low beam headlamp. Refer to Headlamp Assembly or Headlamp Bulb Replacement .

Did you complete the replacement?

Go to Step 18

--

15

Replace the headlamp switch. Refer to Headlamp Switch Replacement .

Did you complete the replacement?

Go to Step 18

--

16

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

Did you complete the replacement?

Go to Step 18

--

17

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 18

--

18

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 3