GM Service Manual Online
For 1990-2009 cars only

Step

Action

Value(s)

Yes

No

1

Was the Headlights System Check performed?

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Go to Step 2

Go to Diagnostic System Check - Lighting Systems

2

  1. Connect a Scan Tool to the data link connector (DLC).
  2. Inspect the IPC input: twilight switch.

Does the twilight sentinel enable switch operate properly?

--

Go to Step 3

Go to Step 7

3

  1. Select the twilight photo from the IPC data list.
  2. Cover the ambient light sensor.

Is the twilight photo value near the specified value?

255 counts

Go to Step 4

Go to Step 6

4

Expose the ambient light sensor to bright sunlight or a very bright incandescent light.

Is the twilight photo value near the specified value?

0 counts

Go to Step 5

Go to Step 6

5

  1. Verify that the symptom still exists.
  2. If the symptom still exists, replace the IPC. Refer to Instrument Cluster Replacement in Instrument Panel, Gauges and Console.

Is the repair complete?

--

Go to Diagnostic System Check - Lighting Systems

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6

Inspect CKT 279 (BLK) for an open or short to voltage. Refer to Testing for Continuity in Wiring Systems.

Is CKT 279 OK?

--

Go to Step 11

Go to Step 13

7

  1. Disconnect the headlamp switch connector C1.
  2. Connect a fused jumper between the headlamp switch connector C1 terminal K (YEL/BLK) and ground.

Is the twilight enable switch input on?

--

Go to Step 9

Go to Step 8

8

Inspect CKT 151 (BLK/WHT) for an open between the headlamp switch and S216. Refer to Testing for Continuity in Wiring Systems.

Is CKT 151 OK?

--

Go to Step 10

Go to Step 13

9

Repair the open in CKT 1784 (YEL/BLK). Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Diagnostic System Check - Lighting Systems

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10

Replace the headlamp switch. Refer to Headlamp Switch Replacement .

Is the repair complete?

--

Go to Diagnostic System Check - Lighting Systems

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11

Inspect CKT 278 (WHT) for an open or short to ground. Refer to Testing for Continuity in Wiring Systems.

Is CKT 278 OK?

--

Go to Step 12

Go to Step 13

12

Replace the ambient light sensor.

Is the repair complete?

--

Go to Diagnostic System Check - Lighting Systems

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13

Repair the suspect wiring. Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Diagnostic System Check - Lighting Systems

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