GM Service Manual Online
For 1990-2009 cars only

Rear Window Defogger Inoperative SUV

Step

Action

Yes

No

Schematic Reference: Defogger Schematics

Connector End View Reference: Stationary Windows Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

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 left side of 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 DEFOG relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a test lamp between the battery positive voltage circuit of the 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 voltage circuit of the 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 left side of 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 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 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 Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 15

--

14

Replace the DEFOG relay. Refer to Relay Replacement in Wiring Systems.

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

Rear Window Defogger Inoperative SUT

Step

Action

Yes

No

Schematic Reference: Defogger Schematics

Connector End View Reference: Stationary Windows Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

  1. Perform the reinitialization of the midgate control module. Refer to Midgate Window Learn Cycle in Body Rear End.
  2. Ensure that the midgate is completely closed and that the midgate ajar indicator is not illuminated.

Is the midgate ajar indicator illuminated when the midgate is completely closed?

Refer to Symptoms - Body Rear End in Body Rear End

Go to Step 3

3

  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 4

Go to Step 11

4

Connect a test lamp between the voltage supply side of the rear window defogger grid and a good ground.

Does the test lamp illuminate?

Go to Step 5

Go to Step 6

5

Connect a test lamp between the voltage supply side of the rear window defogger grid and the ground 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 13

6

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

Does the test lamp illuminate?

Go to Step 7

Go to Step 9

7

  1. Connect a 40-amp fused jumper between the battery voltage circuit of the 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 voltage supply side of the rear window defogger grid and a good ground.

Does the test lamp illuminate?

Go to Step 12

Go to Step 8

8

Test for an open, high resistance, or short to ground in all of the rear window defogger supply voltage circuits on both sides of the midgate control module. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct a condition?

Go to Step 18

Go to Step 10

9

Test the battery positive voltage circuit of the 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 18

Go to Step 14

10

Inspect for poor connection at the harness connector of the midgate 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 18

Go to Step 15

11

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 18

Go to Step 16

12

Inspect for poor connection at the 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 18

Go to Step 17

13

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 18

--

14

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 18

--

15

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

Did you complete the replacement?

Go to Step 18

--

16

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

Did you complete the replacement?

Go to Step 18

--

17

Replace the DEFOG relay. Refer to Relay Replacement in Wiring Systems.

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 2