GM Service Manual Online
For 1990-2009 cars only

Diagnostic Aids

The defogger indicator has its own feed circuit. If this circuit is open the defogger indicator will be inoperative but the defogger will operate.

The defogger relay control circuit and the defogger indicator circuit share the same ground circuit. An open in this circuit will cause the defogger and the defogger indicator to be inoperative.

Step

Action

Yes

No

Schematic Reference: Defogger Schematics

Connector End View Reference: Refer to Component Connector End Views

1

Did you review the Rear Window Defogger Description and Operation and perform the necessary inspections?

Go to Step 2

Go to Symptoms - Fixed and Moveable Windows

2

  1. Start the engine.
  2. Depress the defogger switch.
  3. Observe the defogger indicator.

Does the defogger indicator illuminate?

Go to Step 4

Go to Step 3

3

Does the defogger grid warm?

Go to Step 12

Go to Step 11

4

Command the defogger relay ON and OFF, by depressing the defogger switch.

Do you hear a click when you command the defogger relay ON and OFF?

Go to Step 6

Go to Step 5

5

  1. Exchange the defogger relay with the headlamp relay from the underhood fuse block.
  2. Start the engine.
  3. Command the defogger relay ON and OFF, by depressing the defogger switch.

Do you hear a click when you command the defogger relay ON and OFF?

Go to Step 14

Go to Step 10

6

Depress the defogger switch to the ON position.

Does the defogger grid warm?

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 7

7

  1. Connect a test lamp across the defogger grid terminals.
  2. Start the engine.
  3. Depress the defogger switch.

Does the test lamp illuminate?

Go to Step 17

Go to Step 8

8

Test the defogger grid ground circuit for an open. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 18

Go to Step 9

9

Test the defogger grid supply voltage circuit for an open. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 18

--

10

Test the defogger relay control circuit for an open. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 18

Go to Step 11

11

Test the defogger switch ground circuit for an open. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 18

Go to Step 13

12

Test the defogger indicator supply voltage circuit for an open. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 18

Go to Step 13

13

Inspect for a poor connection at the harness connector of the defogger switch. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 18

Go to Step 15

14

Inspect for a poor connection at the defogger relay connector. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 18

Go to Step 16

15

Replace the defogger switch. Refer to Rear Window Defogger Switch Replacement .

Did you complete the replacement?

Go to Step 18

--

16

Replace the defogger relay.

Did you complete the replacement?

Go to Step 18

--

17

Replace the rear glass. Refer to Liftgate Window Replacement .

Did you complete the replacement?

Go to Step 18

--

18

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 3