GM Service Manual Online
For 1990-2009 cars only

Step

Action

Yes

No

Schematic Reference: Defogger Schematics

Connector End View Reference: Stationary Windows Connector End Views

DEFINITION: The rear window defogger is completely inoperative. No part of the rear window is heated.

1

Did you review the operation of the rear window defogger system and perform the necessary inspections?

Go to Step 2

Go to Symptoms - Stationary Windows

2

  1. Turn ON the ignition, with the engine OFF.
  2. Depress the rear window defogger switch.
  3. Observe the rear window defogger indicator on the HVAC control assembly.

Does the indicator illuminate?

Go to Step 3

Go to Step 5

3

Connect a test lamp between the rear window defogger supply voltage circuit and ground.

Does the test lamp illuminate?

Go to Step 4

Go to Step 9

4

Connect a test lamp between the left side and the right side of the rear window defogger grid.

Does the test lamp illuminate?

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

Go to Step 11

5

  1. Turn OFF the ignition.
  2. Disconnect the harness connector of the HVAC control assembly.
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a test lamp between the battery positive voltage circuit of the HVAC control assembly and ground.

Does the test lamp illuminate?

Go to Step 6

Go to Step 8

6

Connect a test lamp between the ignition voltage circuit of the HVAC control assembly and ground.

Does the test lamp illuminate?

Go to Step 7

Go to Step 13

7

Connect a test lamp between the ignition circuit of the HVAC control assembly and the ground circuit of the HVAC control assembly.

Does the test lamp illuminate?

Go to Step 10

Go to Step 14

8

Test the battery positive voltage circuit of the HVAC control assembly for an open or short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 16

Go to Step 12

9

Test the supply voltage circuit of the rear window defogger for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 16

Go to Step 10

10

Inspect for poor connections at the harness connector of the HVAC control assembly. 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 16

Go to Step 15

11

Repair an open or a high resistance in the ground circuit of the rear window defogger. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 16

--

12

Repair a short to ground in the supply voltage circuit of the rear window defogger. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 16

--

13

Repair an open or a high resistance in the ignition voltage circuit of the HVAC control assembly. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 16

--

14

Repair an open or a high resistance in the ground circuit of the HVAC control assembly. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 16

--

15

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

Did you complete the replacement?

Go to Step 16

--

16

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 2