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For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 Jimmy - 4WD 🢒 Body and Accessories 🢒 Stationary Windows 🢒 Rear Window Defogger Inoperative

Rear Window Defogger Inoperative w/oC68

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 Rear Window Defogger system operation 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 rear window defogger indicator illuminate?

Go to Step 3

Go to Step 5

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 7

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 15

5
  1. Turn OFF the ignition.
  2. Disconnect the harness connector C5 of the HVAC Control Assembly.
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a test lamp between the ignition voltage circuit of the HVAC Control Assembly and a good ground.

Does the test lamp illuminate?

Go to Step 6

Go to Step 16

6

Connect a test lamp between the ignition voltage circuit of the HVAC Control Assembly and the ground circuit of the HVAC Control Assembly.

Does the test lamp illuminate?

Go to Step 12

Go to Step 17

7

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

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

Go to Step 10

Go to Step 8

8
  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 voltage circuit of the RR DEFOG relay coil and a good ground.

Does the test lamp illuminate?

Go to Step 9

Go to Step 18

9
  1. Connect a test lamp between the ignition 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 14

Go to Step 12

10
  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 switched input and a good ground.

Does the test lamp illuminate?

Go to Step 11

Go to Step 19

11
  1. Connect a 30 amp fused jumper wire between the battery positive voltage circuit of the RR DEFOG relay switched input and the relay switched outputr to the supply voltage circuit of the rear window defogger grid.
  2. Connect a test lamp between the rear window defogger grid and a good ground.

Does the test lamp illuminate?

Go to Step 14

Go to Step 20

12

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

Did you find and correct the condition?

Go to Step 23

Go to Step 13

13

Inspect for a poor connection 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 23

Go to Step 21

14

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 23

Go to Step 22

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 23

--

16

Repair an open or short to ground 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 23

--

17

Repair an open or 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 23

--

18

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

Did you complete the repair?

Go to Step 23

--

19

Repair an open or high resistance in the battery positive voltage circuit of the RR DEFOG relay switched input. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 23

--

20

Repair an open or short to ground in the supply voltage circuit of the rear window defogger grid. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 23

--

21

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

Did you complete the replacement?

Go to Step 23

--

22

Replace the RR DEFOG relay.

Did you complete the replacement?

Go to Step 23

--

23

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/C68

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

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 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 13

5

  1. Select from the special functions, under Miscellaneous Test, the Rear Defogger from the HVAC Control Module output controls.
  2. With a scan tool, command the RR DEFOG relay ON and OFF.

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

Does the test lamp illuminate?

Go to Step 7

Go to Step 14

7
  1. Connect a test lamp between the control circuit of the RR DEFOG relay and the ignition voltage circuit of the RR DEFOG relay coil.
  2. With a scan tool, command the RR DEFOG relay ON.

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. 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 9

Go to Step 15

9
  1. Connect a 30 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 12

Go to Step 16

10

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

Did you find and correct the condition?

Go to Step 19

Go to Step 11

11

Inspect for poor connections 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 19

Go to Step 17

12

Inspect for poor connections 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 19

Go to Step 18

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 19

--

14

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

Did you complete the repair?

Go to Step 19

--

15

Repair an open or high resistance in the battery positive voltage circuit of the RR DEFOG relay switched input. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 19

--

16

Repair an open or 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 19

--

17

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

Did you complete the replacement?

Go to Step 19

--

18

Replace the RR DEFOG relay.

Did you complete the replacement?

Go to Step 19

--

19

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 2