GM Service Manual Online
For 1990-2009 cars only

Step

Action

Values

Yes

No

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?

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Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

  1. Turn the ignition to the OFF position.
  2. Turn the headlamp switch to the HEAD position.
  3. Turn the headlamp switch to the OFF position.
  4. 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 bright incandescent lamp.

Do the high beam or low beam headlamps illuminate?

--

Go to Step 8

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

6

  1. Remove the automatic headlamp relay.
  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 bright 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

Go to Step 20

Go to Step 19

9

  1. Turn OFF the ignition.
  2. Disconnect the fuse block - underhood connector C2.
  3. Using a test lamp connected to battery positive voltage, probe the high beam signal circuit that supplies the fuse block - underhood.

Does the test lamp illuminate?

--

Go to Step 11

Go to Step 10

10

Test for a short to ground in the headlamp high beam signal 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 21

Go to Step 16

11

Test for a short to ground 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 21

Go to Step 17

12

Test for a short to ground in the headlamp low beam signal 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 21

Go to Step 13

13

Test for a short to ground 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 21

Go to Step 16

14

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

Did you complete the repair?

--

Go to Step 21

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15

Replace the automatic headlamp relay. Refer to Relay Replacement in Wiring Systems.

Did you complete the repair?

--

Go to Step 21

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16

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

Did you complete the repair?

--

Go to Step 21

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17

Replace the headlamp dimmer switch. Refer to Turn Signal Multifunction Switch Replacement in Steering Wheel and Column.

Did you complete the repair?

--

Go to Step 21

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18

Replace the headlamp switch. Refer to Headlamp Switch Replacement .

Did you complete the repair?

--

Go to Step 21

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19

Replace the ambient light sensor. Refer to Daytime Running Lamp (DRL) Ambient Light Sensor Replacement .

Did you complete the repair?

--

Go to Step 21

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20

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

Did you complete the repair?

--

Go to Step 21

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21

Operate the system in order to verify the repair.

Did you correct the condition?

--

System OK

Go to Step 2