GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1998 🢒 Sonoma Pickup - 4WD 🢒 Body and Accessories 🢒 Stationary Windows 🢒 Rear Window Defogger Inoperative

Step

Action

Value(s)

Yes

No

1

Perform the Defogger System Check.

Was the Defogger System Check performed?

--

Go to Step 2

Go to Defogger System Check

2

Inspect the RR DFOG fuse and the IGN E fuse in the underhood bussed electrical connector (UBEC).

Is either fuse open?

--

Go to Step 26

Go to Step 3

3

Examine the heater and A/C controls.

Is the vehicle equipped with electronic climate control?

--

Go to Step 4

Go to Step 6

4
  1. Connect a scan tool
  2. Check for electronic climate control diagnostic trouble codes (DTCs).

Were there any climate control DTCs?

--

Go to Step 5

Go to Step 11

5

Use the appropriate DTC table to locate the cause of the DTC.

Did you complete the repair?

--

Go to Defogger System Check

--

6

Inspect the HVAC I fuse in the IP fuse block.

Is the fuse open?

--

Go to Step 26

Go to Step 7

7
  1. Turn ON the ignition with the engine OFF.
  2. Measure the voltage at the HVAC I fuse.

Is the voltage within the specified range?

9-16 V

Go to Step 9

Go to Step 8

8

Repair the power supply circuit for the HVAC I fuse.

Did you complete the repair?

--

Go to Defogger System Check

--

9
  1. Turn ON the ignition with the engine OFF.
  2. Measure the voltage at C5 terminal 2 of the Heater And A/C Controller.

Is the voltage within the specified range?

9-16 V

Go to Step 11

Go to Step 10

10

Repair the open in CKT 341.

Did you complete the repair?

--

Go to Defogger System Check

--

11
  1. Turn ON the ignition with the engine OFF.
  2. Turn on the rear window defogger
  3. Measure the voltage at the endgate liftgate, CKT 1093.

Is the voltage within the specified range?

9-16 V

Go to Step 27

Go to Step 12

12
  1. Turn ON the ignition with the engine OFF.
  2. Turn on the rear window defogger.
  3. Measure the voltage at the RR DFOG fuse.

Is the voltage within the specified range?

9-16 V

Go to Step 13

Go to Step 14

13

Locate and repair the open in CKT 1093 between the RR DFOG fuse and the rear window defogger grid.

Did you complete the repair?

--

Go to Defogger System Check

--

14
  1. Remove the rear defogger relay.
  2. Locate pin 30 on the rear defogger relay.
  3. Measure the voltage at the UBEC connector for pin 30.

Is the voltage within the specified range?

9-16 V

Go to Step 16

Go to Step 15

15

Repair the power supply circuit for terminal 30 of the rear defogger relay.

Did you complete the repair?

--

Go to Defogger System Check

--

16
  1. With the rear defogger removed, locate pin 86 on the rear defogger relay.
  2. Measure the voltage at the UBEC connector for pin 86.

Is the voltage within the specified range?

9-16 V

Go to Step 18

Go to Step 17

17

Repair the power supply circuit for terminal 86 of the rear defogger relay.

Did you complete the repair?

--

Go to Defogger System Check

--

18

Measure the resistance between terminals 85 and 86 of the Rear Defogger Relay.

Does the resistance measurement indicate continuity between terminals 85 and 86?

--

Go to Step 20

Go to Step 19

19

Replace the rear defogger relay.

Did you complete the repair?

--

Go to Defogger System Check

--

20
  1. Install the rear defogger relay.
  2. Turn the ignition ON with the engine OFF.
  3. Turn on the rear window defogger .
  4. Perform the following procedure:
    • For manual A/C, measure the voltage at the heater and A/C controller, cavity 3 of connector C5.
    • For automatic A/C, measure the voltage at the electronic climate control module connector D14.

Is the voltage within the specified range?

9-16 V

Go to Step 22

Go to Step 21

21

Repair the open in CKT 193.

Did you complete the repair?

--

Go to Defogger System Check

--

22
  1. Remove the rear defogger relay.
  2. Connect a fused jumper wire between the UBEC connectors for terminals 30 and 87 of the rear defogger relay.
  3. Turn ON the ignition with the engine OFF.
  4. Turn of the rear window defogger.

Does the rear window defogger function correctly?

Go to Step 19

Go to Step 23

23

Measure the resistance of CKT 1050.

Was CKT 1050 open?

--

Go to Step 25

Go to Step 24

24

Repair the open in CKT 1050.

Did you complete the repair?

--

Go to Defogger System Check

--

25
    • With manual A/C, replace the Heater And A/C Controller.
    • With electronic A/C, replace the Electronic Climate Control Module.

Did you complete the repair?

--

Go to Defogger System Check

--

26

Locate and repair the short to ground.

Did you complete the repair?

--

Go to Defogger System Check

--

27

Measure the resistance of CKT 1450.

Was CKT 1450 open?

--

Go to Step 28

Go to Step 29

28

Locate and repair the open in CKT 1450.

Did you complete the repair?

--

Go to Defogger System Check

--

29

Repair the rear window defogger grid.

Did you complete the repair?

--

Go to Defogger System Check

--