GM Service Manual Online
For 1990-2009 cars only

Step

Action

Value(s)

Yes

No

Schematic Reference: Exterior Lights Schematics

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

1

Did you perform the Diagnostic System Check - Vehicle?

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Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

Important: Vehicle shift lever must be out of the PARK position and the parking brake disengaged in order for the daytime running lamps (DRL) to operate.

  1. Verify the headlamp switch is in the OFF position.
  2. Turn ON the ignition, with the engine OFF.
  3. Place the twilight switch to the MAX position.
  4. Depress and hold the brake pedal.
  5. Move the gear selector out of the PARK position.
  6. Verify the parking brake is disengaged.
  7. Expose the ambient light sensor to a bright light.
  8. Wait about 20 seconds.
  9. Observe the DRL lamps.
  10. Cover the ambient light sensor.
  11. Wait about 20 seconds.
  12. Observe the DRL lamps.
  13. Place the gear selector in the PARK position.
  14. Release the brake pedal.

Do the headlamps switch between low beam and DRL?

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

Go to Step 3

3

Do the headlamps operate properly?

--

Go to Step 4

Go to Headlamps Inoperative - Low Beams or Headlamps Inoperative - High Beams

4

  1. Turn OFF the ignition.
  2. Disconnect the lamp control module (LCM).
  3. Connect a test lamp between the ignition 1 voltage circuit at the LCM connector and ground.
  4. Turn ON the ignition, with the engine OFF.

Does the test lamp illuminate?

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Go to Step 5

Go to Step 14

5

  1. Turn OFF the ignition.
  2. Connect a DMM between the twilight sentinel delay signal circuit at the LCM connector and a good ground.
  3. Vary the twilight delay control from MIN to MAX.

Does the resistance vary within the specified range?

3.5K-200K ohms

Go to Step 6

Go to Step 8

6

  1. Cover the ambient light sensor.
  2. Connect a DMM between ambient light sensor signal circuit at the LCM connector and a good ground.

Is the resistance greater than the specified value?

31K ohms

Go to Step 7

Go to Step 9

7

Expose the ambient light sensor to a bright light.

Is the resistance less than the specified value?

23K ohms

Go to Step 13

Go to Step 9

8

Test the twilight sentinel delay signal circuit for high resistance, an open, or a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

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Go to Step 18

Go to Step 11

9

Test the ambient light sensor ground circuit for an open or a high resistance. 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

10

Test the ambient light sensor signal circuit for a high resistance, an open, or a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

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Go to Step 18

Go to Step 12

11

Inspect for 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?

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Go to Step 18

Go to Step 15

12

Inspect for poor connections at the harness connector of the ambient light sensor. 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

13

Inspect for poor connections at the harness connector of the LCM. 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

14

Repair the open or short to ground in the ignition 1 voltage circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 18

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15

Replace the headlamp switch. Refer to Headlamp Switch Replacement .

Did you complete the replacement?

--

Go to Step 18

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16

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

Did you complete the replacement?

--

Go to Step 18

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17

Replace the LCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 18

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18

Operate the system in order to verify the repair.

Did you correct the condition?

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System OK

Go to Step 2