GM Service Manual Online
For 1990-2009 cars only

Step

Action

Values

Yes

No

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

1

Did you perform the Lighting System Diagnostic System Check?

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Go to Step 2

Go to Diagnostic System Check - Lighting Systems

2

  1. Turn the ignition to the OFF position.
  2. Turn the headlamp switch to the OFF position.
  3. Place the headlamp dimmer switch in the low beam position.

Do the low beams headlamps illuminate?

--

Go to Step 3

Go to Step 4

3

Place the headlamp dimmer switch in the high beam position.

Do the high beams headlamps illuminate?

--

Go to Step 6

Go to Step 12

4

Are the high beam headlamps on at all times?

--

Go to Step 9

Go to Step 5

5

  1. Turn the ignition to the ON position.
  2. Expose the ambient light sensor to a strong incandescent lamp.

Do the high beam or low beam headlamps illuminate?

--

Go to Step 8

Go to Testing for Intermittent Conditions and Poor Connections

6

  1. Disconnect the automatic headlamp control module.
  2. Place the headlamp dimmer switch in the low beam position.
  3. Place the headlamp dimmer switch in the high beam position.

Do the high beam and low beam headlamps illuminate?

--

Go to Step 7

Go to Step 15

7

  1. Disconnect the headlamp switch.
  2. Place the headlamp dimmer switch in the low beam position.
  3. Place the headlamp dimmer switch in the high beam position.

Do the high beam and low beam headlamps illuminate?

--

Go to Step 14

Go to Step 18

8

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. Expose the ambient light sensor to a strong incandescent lamp.
  4. With a scan tool, observe the ambient light sensor parameter in the Body Control Module (BCM) data list.

Does the scan tool indicate that the ambient light sensor input parameter is within the specified range?

0.5 - 2.5 Volts

Go to Step 15

Go to Step 19

9

  1. Turn OFF the ignition.
  2. Disconnect the underhood junction block connector C2.
  3. Probe the high beam signal circuit of the underhood junction block connector with a test lamp that is connected to good ground.

Does the test lamp illuminate

--

Go to Step 11

Go to Step 10

10

Test for a short to battery voltage in the high beam supply voltage circuit of the LH and RH headlamps. 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

11

Test for a short to battery voltage in the high beam signal circuit 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 17

12

Test for a short to battery voltage in the low beam supply voltage circuits of the LH and RH headlamps. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 20

Go to Step 13

13

Test for a short to battery voltage in the low beam signal circuit 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 16

14

Repair a short to battery voltage in the headlamp switch signal circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 20

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15

Replace the automatic headlamp control module. Refer to Headlamp Control Module Replacement

Did you complete the repair?

--

Go to Step 20

--

16

Replace the underhood junction block. Refer to Underhood Electrical Center or Junction Block Replacement in Wiring Systems.

Did you complete the repair?

--

Go to Step 20

--

17

Replace the headlamp dimmer switch.

Refer to Multifunction, Turn Signal, and Hazard Switch Replacement - On Vehicle in Steering Wheel and Column - Tilt.

Did you complete the repair?

--

Go to Step 20

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18

Replace the headlamp switch. Refer to Headlamp Switch Replacement .

Did you complete the repair?

--

Go to Step 20

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19

Replace the ambient light sensor. Refer to Ambient Light Sensor Replacement

Did you complete the repair?

--

Go to Step 20

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20

Operate the system in order to verify the repair.

Did you correct the condition?

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System OK

Go to Step 2