GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2000 🢒 Blazer - 4WD 🢒 Body and Accessories 🢒 Stationary Windows 🢒 Rear Window Defogger Inoperative

Step

Action

Value(s)

Yes

No

1

Did you review the rear window defogger circuit description and perform the necessary inspections?

--

Go to Step 2

Go to Symptoms

2

Verify that the rear window defoggers are inoperative.

Does the rear window defogger operate normally?

--

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 3

3

Inspect the RR DFOG fuse and the IGN E fuse in the underhood fuse block.

Is either fuse open?

--

Go to Step 27

Go to Step 4

4

Examine the heater and A/C controls.

Is the vehicle equipped with electronic climate control (ECC)?

--

Go to Step 5

Go to Step 7

5
  1. Connect a scan tool
  2. Check for ECC diagnostic trouble codes (DTCs).

Were there any ECC DTCs?

--

Go to Step 6

Go to Step 12

6

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

Did you complete the repair?

--

Go to Step 31

--

7

Inspect the HVAC I fuse in the IP fuse block.

Is the fuse open?

--

Go to Step 27

Go to Step 8

8
  1. Turn ON the ignition with the engine OFF.
  2. Measure the voltage at the HVAC I fuse.

Does the voltage measure near the specified value?

B+

Go to Step 10

Go to Step 9

9

Repair the power supply circuit for the HVAC I fuse.

Did you complete the repair?

--

Go to Step 31

--

10
  1. Turn ON the ignition with the engine OFF.
  2. Measure the voltage at C5 terminal 2 of the heater and A/C controller.

Does the voltage measure near the specified value?

B+

Go to Step 12

Go to Step 11

11

Repair the open in CKT 341.

Did you complete the repair?

--

Go to Step 31

--

12
  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.

Does the voltage measure near the specified value?

B+

Go to Step 28

Go to Step 13

13
  1. Turn ON the ignition with the engine OFF.
  2. Turn on the rear window defogger grid.
  3. Measure the voltage at the RR DFOG fuse.

Does the voltage measure near the specified value?

B+

Go to Step 14

Go to Step 15

14

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 Step 31

--

15
  1. Remove the rear window defogger relay.
  2. Locate pin 30 on the rear window defogger relay.
  3. Measure the voltage at the underhood fuse block connector for pin 30.

Does the voltage measure near the specified value?

B+

Go to Step 17

Go to Step 16

16

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

Did you complete the repair?

--

Go to Step 31

--

17
  1. With the rear window defogger removed, locate pin 86 on the rear window defogger relay.
  2. Measure the voltage at the underhood fuse block connector for pin 86.

Does the voltage measure near the specified value?

B+

Go to Step 19

Go to Step 18

18

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

Did you complete the repair?

--

Go to Step 31

--

19

Measure the resistance between terminals 85 and 86 of the rear window defogger relay.

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

--

Go to Step 21

Go to Step 20

20

Replace the rear window defogger relay.

Did you complete the repair?

--

Go to Step 31

--

21
  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.

Does the voltage measure near the specified value?

B+

Go to Step 23

Go to Step 22

22

Repair the open in CKT 193.

Did you complete the repair?

--

Go to Step 31

--

23
  1. Remove the rear window defogger relay.
  2. Connect a fused jumper wire between the underhood fuse block connectors for terminals 30 and 87 of the rear window defogger relay.
  3. Turn ON the ignition with the engine OFF.
  4. Turn off the rear window defogger grid.

Does the rear window defogger grid function correctly?

--

Go to Step 20

Go to Step 24

24

Measure the resistance of CKT 1050.

Was CKT 1050 open?

--

Go to Step 26

Go to Step 25

25

Repair the open in CKT 1050.

Did you complete the repair?

--

Go to Step 31

--

26
    • With manual A/C, replace the heater and A/C controller.
    • With electronic A/C, replace the ECC.

Did you complete the repair?

--

Go to Step 31

--

27

Locate and repair the short to ground.

Did you complete the repair?

--

Go to Step 31

--

28

Measure the resistance of CKT 1450.

Was CKT 1450 open?

--

Go to Step 29

Go to Step 30

29

Locate and repair the open in CKT 1450.

Did you complete the repair?

--

Go to Step 31

--

30

Repair the rear window defogger grid.

Did you complete the repair?

--

Go to Step 31

--

31

Operate the system in order to verify the repair.

Did you find and correct the condition?

--

System OK

Go to Step 3