GM Service Manual Online
For 1990-2009 cars only

Step

Action

Values

Yes

No

1

Test the rear window defogger.

Does the rear window defogger work?

--

Go to Step 4

Go to Step 2

2

Repair the rear window defogger before proceeding with the outside rearview mirror diagnosis.

Is the repair complete?

--

Go to Step 3

--

3

Test the outside rearview mirror defoggers.

Does the repair of the rear window defogger system also fix the condition with the outside rearview mirror defoggers?

--

System OK

Go to Step 4

4

Test fuses E21 and F19.

Are fuses E21 or F19 open?

--

Go to Step 5

Go to Step 6

5

  1. Test for a short circuit and repair if necessary.
  2. Replace the fuse.

Is the repair complete?

--

System OK

--

6

  1. On the side of the vehicle that has the malfunctioning defogger, remove the black plastic plate from the trim panel side of the door.
  2. Disconnect the electrical connector from the outside rearview mirror.
  3. Turn ON the ignition.
  4. Turn ON the defogger.
  5. Using a voltmeter, backprobe terminal 2 (ORN) at the electrical connector to the outside rearview mirror.

Does the voltmeter indicate the specified value?

11-14 V

Go to Step 9

Go to Step 7

7

Repair the open circuit between fuse E21 and the defogger relay.

Is the repair complete?

--

System OK

Go to Step 8

8

  1. Turn ON the ignition.
  2. Turn ON the defogger.
  3. Use a voltmeter to fuse F19 and the defogger relay terminal 86.

Does the voltmeter indicate the specified value?

11-14 V

Go to Step 10

Go to Step 9

9

Replace the defogger switch.

Is the repair complete?

--

System OK

--

10

Replace the defogger relay.

Does the outside rearview mirror work?

--

System OK

Go to Step 11

11

  1. Turn OFF the ignition.
  2. Disconnect the electrical connector to the outside rearview mirror.
  3. Use an ohmmeter to measure the resistance between terminal 1 (BLK) of the outside rearview mirror connector and ground.

Does the ohmmeter indicate the specified value?

0 ohms

Go to Step 13

Go to Step 12

12

Repair the open ground circuit for the outside rearview mirror.

Is the repair complete?

--

System OK

--

13

Replace the defective outside rearview mirror.

Is the repair complete?

--

System OK

--