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For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 GMC C Sierra - 2WD 🢒 Body and Accessories 🢒 Doors 🢒 Rear Window Defogger Inoperative

Rear Window Defogger Inoperative w/o Cargo Doors

Test Description

The number below refers to the step number on the diagnostic table.

  1. Listen for an audible click when the RR DEFOG relay operates. Command both the ON and OFF states of the RR DEFOG relay. Repeat the commands as necessary.

Step

Action

Yes

No

Schematic Reference: Defogger Schematics

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 Module.

Does the rear window defogger indicator illuminate?

Go to Step 3

Go to Step 10

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 14

5

Command the RR DEFOG relay ON and OFF, by depressing the rear window defogger switch on the HVAC Control Module.

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

Go to Step 8

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 ignition 1 voltage circuit of the RR DEFOG relay coil and a good ground.

Does the test lamp illuminate?

Go to Step 7

Go to Step 15

7
  1. Connect a test lamp between the ignition 1 voltage circuit of the RR DEFOG relay coil and the control circuit of the RR DEFOG relay.
  2. Depress the rear window defogger switch.

Does the test lamp illuminate?

Go to Step 12

Go to Step 10

8
  1. Turn OFF the ignition.
  2. Disconnect the RR DEFOG relay.
  3. Connect a test lamp between the battery positive voltage circuit of the RR DEFOG relay switch and a good ground.

Does the test lamp illuminate?

Go to Step 9

Go to Step 11

9
  1. Connect a 30 amp fused jumper wire between the battery positive voltage circuit of the RR DEFOG relay switch and 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 12

Go to Step 17

10

Test the control circuit of the RR DEFOG relay for an open or short to battery positive voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 20

Go to Step 13

11

Test the battery positive circuit of the RR DEFOG relay switch 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 20

Go to Step 16

12

Inspect for a 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 20

Go to Step 18

13

Inspect for a 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 20

Go to Step 19

14

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

Did you complete the repair?

Go to Step 20

--

15

Repair an open or high resistance in the ignition 1 voltage circuit of the RR DEFOG relay coil. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 20

--

16

Repair the 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 20

--

17

Repair an open or high resistance 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 20

--

18

Replace the RR DEFOG relay.

Did you complete the replacement?

Go to Step 20

--

19

Replace the HVAC Control Module. Refer to Heater and Air Conditioning Control Replacement in HVAC Systems - Manual or HVAC Control Module Replacement in HVAC Systems - Automatic.

Did you complete the replacement?

Go to Step 20

--

20

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/Cargo Doors

Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

  1. Listen for an audible click when the RR DEFOG relay operates. Command both the ON and OFF states of the RR DEFOG relay. Repeat the commands as necessary.

Step

Action

Yes

No

Schematic Reference: Defogger Schematics

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 Module.

Does the rear window defogger indicator illuminate?

Go to Step 3

Go to Step 11

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 15

5

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

Go to Step 16

Go to Step 6

6

Command the RR DEFOG relay ON and OFF, by depressing the rear window defogger switch on the HVAC Control Module.

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

Go to Step 9

Go to Step 7

7
  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 ignition 1 voltage circuit of the RR DEFOG relay coil and a good ground.

Does the test lamp illuminate?

Go to Step 8

Go to Step 17

8
  1. Connect a test lamp between the ignition 1 voltage circuit of the RR DEFOG relay coil and the control circuit of the RR DEFOG relay.
  2. Depress the rear window defogger switch.

Does the test lamp illuminate?

Go to Step 13

Go to Step 11

9
  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 switch and a good ground.

Does the test lamp illuminate?

Go to Step 10

Go to Step 12

10
  1. Connect a 30 amp fused jumper wire between the battery positive voltage circuit of the RR DEFOG relay switch and 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 13

Go to Step 16

11

Test the control circuit of the RR DEFOG relay for an open or short to battery positive voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 21

Go to Step 14

12

Test the battery positive voltage circuit of the RR DEFOG relay coil 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 21

Go to Step 18

13

Inspect for a 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 21

Go to Step 19

14

Inspect for a 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 21

Go to Step 20

15

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

Did you complete the repair?

Go to Step 21

--

16

Repair an open or high resistance 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 21

--

17

Repair an open or high resistance in the ignition 1 voltage circuit of the RR DEFOG relay coil. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 21

--

18

Repair the 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 21

--

19

Replace the RR DEFOG relay.

Did you complete the replacement?

Go to Step 21

--

20

Replace the HVAC Control Module. Refer to Heater and Air Conditioning Control Replacement in HVAC Systems - Manual or HVAC Control Module Replacement in HVAC Systems - Automatic.

Did you complete the replacement?

Go to Step 21

--

21

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 2