GM Service Manual Online
For 1990-2009 cars only

Step

Action

Yes

No

Schematic Reference: Interior Lights Dimming Schematics

Connector End View Reference: Master Electrical Component List

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

Verify that the interior backlighting does not dim.

Does the interior backlighting operate normally?

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 3

3

Do the instrument panel (I/P) lamps dim?

Go to Step 13

Go to Step 4

4

Do the class 2 lamps dim?

Go to Step 5

Go to Step 6

5

Test for a short to battery positive voltage in the I/P lamps supply voltage circuit. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 14

Go to Step 13

6

Disconnect the lamp switch assembly.

Does all the illumination of the backlight components turn OFF?

Go to Step 8

Go to Step 7

7

Test for a short to battery positive voltage on the I/P dimming control circuit. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 14

Go to Step 8

8

Test for a poor connection, an open, or a short to ground in the I/P dimming control circuit. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 14

Go to Step 9

9

Test for a poor connection or an open in the I/P dimming return circuit. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 14

Go to Step 10

10

  1. Reconnect the lamp switch assembly.
  2. Disconnect the body control module (BCM) connector C1.
  3. Using a DMM, measure the resistance between the I/P dimming voltage reference circuit and the I/P dimming control circuit.
  4. Vary the I/P dimming switch from full bright to full dim.

Does the DMM, display change?

Go to Step 13

Go to Step 11

11

Test for an open or a short to battery positive voltage in the I/P dimming voltage reference circuit. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 14

Go to Step 12

12

Replace the lamp switch assembly. Refer to Headlamp Switch Replacement .

Did you complete the replacement?

Go to Step 14

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13

Replace the BCM. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 14

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14

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 2