GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1999 🢒 GMC K Sierra - 4WD 🢒 Body and Accessories 🢒 Stationary Windows 🢒 Rear Window Defogger Inoperative

Step

Action

Value(s)

Yes

No

IMPORTANT:

  1. Inspect the condition of IGN E , HVAC and RR defogger fuse. If any fuse is open, locate and repair source of the overload.
  2. Verify that G200, G203 and G306 are clean and tight.

1
  1. Turn the ignition switch to the RUN position.
  2. Connect a test lamp between CKT 1093 (PPL) and ground at the deffoger grid connector.
  3. Press the rear defogger switch once.

Does the test lamp light?

--

Go to Step 2

Go to Step 5

2

Locate the open in CKT 1250 (BLK) between the grid and G306.

Did you find an open?

--

Go to Step 3

Go to Step 4

3

Repair the open in CKT 1250 (BLK) between the grid and G306.

Is the repair complete?

--

Go to Defogger System Check

--

4

Replace the rear window defogger grid. Refer to Grid Line Repair .

Is the repair complete?

--

Go to Defogger System Check

--

5

Connect a test lamp between the RR defogger fuse located in the underhood bussed electrical center (UBEC) and ground.

Does the test lamp light?

--

Go to Step 6

Go to Step 7

6
  1. Locate the open in CKT 1093 (PPL) between the rear window defogger grid and UBEC.
  2. Repair the open.

Is the repair complete?

--

Go to Defogger System Check

--

7
  1. Ensure the test lamp is still connected at the RR defogger fuse.
  2. Gain access to connector C1 at the UBEC.
  3. Connect a fused jumper wire back probe between cavity D9 and ground.

Does the test lamp light?

--

Go to Step 11

Go to Step 8

8
  1. Disconnect the rear window defogger relay.
  2. Using the correct terminal adapter from J 35616 , connect a test lamp from cavity 85 to ground and then from from cavity 30 to ground.

Does the test lamp light in both cavities?

--

Go to Step 9

Go to Step 10

9

Replace the rear window defogger relay.

Is repair complete?

--

Go to Defogger System Check

--

10

Locate and repair the power feed from the power distribution to the rear window defogger relay.

Is the repair complete?

--

Go to Defogger System Check

--

11

Locate the open in CKT 193 (WHT) or CKT 2450 (BLK).

Did you find an open?

--

Go to Step 12

Go to Step 13

12

Repair the open in CKT 193 (WHT) or CKT 2450 (BLK).

Is the repair complete?

--

Go to Defogger System Check

--

13

Replace the rear defog switch (part of the HVAC control module). Refer to Control Assembly Replacement .

Is the repair complete?

--

Go to Defogger System Check

--