GM Service Manual Online
For 1990-2009 cars only

Rear Window Defogger Inoperative w/ Cargo Doors

Step

Action

Yes

No

Schematic Reference: Defogger Schematics

Connector End View Reference: Stationary Windows Connector End Views

1

Did you perform the Defogger Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - Defogger

2

  1. Start the engine.
  2. Depress the rear window defogger switch.
  3. Observe the rear window defogger indicator on the HVAC Control Module.

Does the rear window defogger indicator illuminate?

Go to Step 3

Go to Step 9

3

  1. Connect a test lamp between the rear window defogger grid on the left cargo door and a good ground.
  2. Connect a test lamp between the rear window defogger grid on the right cargo door and a good ground.

Does the test lamp illuminate on both rear window defogger grids?

Go to Step 4

Go to Step 5

4

  1. Connect a test lamp between the left side of the rear window defogger grid and the right side of the rear window defogger grid on the left cargo door.
  2. Connect a test lamp between the left side of the rear window defogger grid and the right side of the rear window defogger grid on the right cargo door.

Does the test lamp illuminate on both rear window defogger grids?

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

Go to Step 11

5

Does the test lamp illuminate on one of the rear window defogger grids?

Go to Step 13

Go to Step 6

6

  1. Turn OFF the ignition.
  2. Disconnect the RR DEFOG relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a test lamp between the battery positive voltage circuit of the RR DEFOG relay switched input and a good ground.

Does the test lamp illuminate?

Go to Step 7

Go to Step 8

7

  1. Connect a 40-ampere fused jumper between the battery positive voltage circuit of the RR DEFOG relay switched input and the relay switched output to the supply voltage circuit of the rear window defogger.
  2. Connect a test lamp between the rear window defogger grid and a good ground.

Does the test lamp illuminate?

Go to Step 10

Go to Step 13

8

Test the battery positive voltage circuit of the RR DEFOG relay switched input 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 12

9

Inspect for poor connection at the harness connector of the HVAC Control Module. 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 14

10

Inspect for poor connection at the RR DEFOG relay. 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 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 high resistance in the supply circuit of the rear window defogger. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 16

--

14

Replace the HVAC Control Module. Refer to HVAC Control Module Replacement in HVAC Systems - Automatic or HVAC Control Module Replacement in HVAC Systems -- Manual.

Did you complete the replacement?

Go to Step 16

--

15

Replace the RR DEFOG relay.

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

Rear Window Defogger Inoperative w/o Cargo Doors

Step

Action

Yes

No

Schematic Reference: Defogger Schematics

Connector End View Reference: Stationary Windows Connector End Views

1

Did you perform the Defogger Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - Defogger

2

  1. Start the engine.
  2. Depress the rear window defogger switch.
  3. Observe the rear window defogger indicator on the HVAC Control Module.

Does the rear window defogger indicator illuminate?

Go to Step 3

Go to Step 8

3

Connect a test lamp between the rear window defogger grid and a good ground.

Does the test lamp illuminate?

Go to Step 4

Go to Step 5

4

Connect a test lamp between the left side of the rear window defogger grid 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 10

5

  1. Turn OFF the ignition.
  2. Disconnect the RR DEFOG relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a test lamp between the battery positive voltage circuit of the RR DEFOG relay switched input and a good ground.

Does the test lamp illuminate?

Go to Step 6

Go to Step 7

6

  1. Connect a 40 amp fused jumper between the battery positive voltage circuit of the RR DEFOG relay switched input and the relay switched output to the supply voltage circuit of the rear window defogger.
  2. Connect a test lamp between the rear window defogger grid and a good ground.

Does the test lamp illuminate?

Go to Step 9

Go to Step 12

7

Test the battery positive voltage circuit of the RR DEFOG relay switched input 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 15

Go to Step 11

8

Inspect for poor connection at the harness connector of the HVAC Control Module. 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 15

Go to Step 13

9

Inspect for poor connection at the RR DEFOG relay. 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 15

Go to Step 14

10

Repair an open or 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 15

--

11

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 15

--

12

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

Did you complete the repair?

Go to Step 15

--

13

Replace the HVAC Control Module. Refer to HVAC Control Module Replacement in HVAC Systems - Automatic or HVAC Control Module Replacement in HVAC Systems -- Manual.

Did you complete the replacement?

Go to Step 15

--

14

Replace the RR DEFOG relay.

Did you complete the replacement?

Go to Step 15

--

15

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 2