GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1999 🢒 Monte Carlo 🢒 Body and Accessories 🢒 Stationary Windows 🢒 Rear Window Defogger Inoperative

Step

Action

Value(s)

Yes

No

1
  1. Turn the ignition switch to the RUN position.
  2. Press and release the rear defogger switch.
  3. Observe if the defogger ON indicator turns ON.

Does the defogger ON indicator turn ON?

--

Go to Step 2

Go to Step 15

2
  1. Remove the rear window defogger relay.
  2. Use a test lamp to backprobe the rear window defogger relay harness connector between terminals A 2 and C 1.

Does the test lamp light?

--

Go to Step 3

Go to Step 8

3

Use a test lamp to backprobe the rear window defogger relay harness connector between terminal C 2 and ground.

Does the test lamp light?

--

Go to Step 4

Go to Step 7

4
  1. Press and release the rear defogger switch again if the rear defogger ON indicator turns OFF before the test is complete.
  2. Use a test lamp to backprobe the rear window defogger relay harness connector between terminals C 2 and A 1.

Does the test lamp light?

--

Go to Step 5

Go to Step 6

5

Inspect for loose terminals at the relay connector and repair if found. If no loose connections are found, replace the defogger relay.

Is the repair complete?

--

System OK

Go To Step 6

6
  1. Repair a poor connection or an open in CKT 292 (LT BLU).
  2. Inspect the system.

Is the repair complete?

--

System OK

Go To Step 23

7
  1. Repair a poor connection or an open in CKT 41 (BRN) between the rear window defogger relay harness connector terminal C 2 and the fuse block terminal D 10.
  2. Inspect the system.

Is the repair complete?

--

System OK

Go To Step 8

8
  1. Press and release the rear defogger switch again if the rear defogger ON indicator turns OFF before the test is complete.
  2. Use a test lamp to backprobe the rear window defogger relay harness connector between terminal A 2 and ground.

Does the test lamp light?

--

Go to Step 9

Go to Step 14

9
  1. Press and release the rear defogger switch again if the rear defogger ON indicator turns OFF before the test is complete.
  2. Use a test lamp to backprobe the rear defogger grid harness connector between CKT 293 (PPL) and CKT 850 (BLK).

Does the test lamp light ?

--

Go to Step 10

Go to Step 11

10
  1. Repair the rear defogger grid. Refer to Grid Line Repair .
  2. Inspect the system.

Is the repair complete?

--

System OK

Go To Step 11

11
  1. Press and release the rear defogger switch again if the rear defogger ON indicator turns OFF before the test is complete.
  2. Use a test lamp to backprobe the rear defogger grid harness connector between CKT 293 (PPL) and ground.

Does the test lamp light?

--

Go to Step 12

Go to Step 13

12
  1. Repair a poor connection or an open in CKT 850 (BLK) between the rear defogger grid and G 301.
  2. Inspect the system.

Is the repair complete?

--

System OK

--

13
  1. Repair a poor connection or an open in CKT 293 (PPL) between the rear window defogger relay connector terminal C 1 and the rear defogger grid connector.
  2. Inspect the system.

Is the repair complete?

--

System OK

Go To Step 14

14
  1. Repair a poor connection or an open in CKT 1040 (ORN) between the fuse block terminal A 2 and the rear window defogger relay harness connector terminal A 2.
  2. Inspect the system.

Is the repair complete?

--

System OK

Go To Step 15

15

Inspect Fuse 4 in the fuse block for an open.

Is the fuse open?

--

Go to Step 16

Go to Step 17

16
  1. Repair the short to ground in CKT 41 (BRN).
  2. Reinspect the system.

Is the repair complete?

--

System OK

Go To Step 17

17
  1. Turn the ignition switch to the RUN position.
  2. Use a test lamp to backprobe the heater-A/C control connector C 2 terminals B 7 and B 8.

Does the test lamp light?

--

Go to Step 18

Go to Step 20

18
  1. Press and release the rear defogger switch.
  2. Use a test lamp to backprobe between the heater-A/C control connector C 2 terminal B 2 and ground.

Does the test lamp light?

--

Go to Step 19

Go to Step 23

19
  1. Repair a short to B+ in CKT 292 (LT BLU).
  2. Inspect the system.

Is the repair complete?

--

System OK

Go To Step 20

20
  1. Use a test lamp to backprobe between the heater-A/C control harness connector C 2 terminal B 7 and ground.
  2. Recheck the system.

Does the test lamp light?

--

Go to Step 21

Go to Step 22

21
  1. Repair a poor connection or an open in CKT 150 (BLK) between the heater-A/C control harness connector C 2 terminal B 7 and G 205.
  2. Inspect the system.

Is the repair complete?

--

System OK

--

22
  1. Repair a poor connection or an open in CKT 41 (BRN) between the fuse block terminal D 10 and the heater-A/C control harness connector C 2 terminal B 7.
  2. Inspect the system.

Is the symptom still present?

--

System OK

--

23

Replace the heater-a/c control. Refer to Control Assembly Replacement in HVAC Systems.

Is the repair complete?

--

System OK

--