GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Oldsmobile 🢒 1999 🢒 Cutlass 🢒 Body and Accessories 🢒 Stationary Windows 🢒 Rear Window Defogger Always On

Step

Action

Value(s)

Yes

No

1

Exchange the rear defogger relay with a known good relay from the underhood wiring harness junction block.

Does the rear defogger grid continue to warm?

--

Go to Step 2

Go to Step 3

2

Disconnect the underhood wiring harness junction block connector C3.

Does the rear defogger grid continue to warm?

--

Go to Step 4

Go to Step 9

3

Replace the faulty relay

Is the repair complete?

--

Go to Defogger System Check

--

4
  1. Disconnect connector C2 of the left instrument panel wiring harness junction block.
  2. Connect a test lamp between terminal C1 of the left instrument panel wiring harness junction block connector C2 and ground.

Does the test lamp light?

--

Go to Step 5

Go to Step 6

5

Repair the short to positive battery voltage in CKT 293 between the underhood wiring harness junction block and the left IP wiring harness junction block. Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Defogger System Check

--

6
  1. Disconnect connector C3 of the left IP wiring harness junction block.
  2. Connect a test lamp between terminal C12 of the left IP wiring harness junction block connector C3 and ground.

Does the test lamp light?

--

Go to Step 7

Go to Step 8

7

Repair the short to positive battery voltage in CKT 293 between the left IP wiring harness junction block and the rear defogger grid. Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Defogger System Check

--

8

Replace the left IP wiring harness junction block.Refer to Relay/Fuse Center Replacement in Wiring Systems

Is the repair complete?

--

Go to Defogger System Check

--

9
  1. Turn the ignition switch to the OFF position.
  2. Use a DMM to measure the resistance between terminal C5 of the underhood wiring harness junction block connector C3 and ground.

Is the resistance measured within the specified range?

Infinite

Go to Step 10

Go to Step 11

10

Replace the underhood wiring harness junction block. Refer to Relay/Fuse Center Replacement in Wiring Systems

Is the repair complete?

--

Go to Defogger System Check

--

11
  1. Disconnect connector C2 of the heater and A/C control assembly.
  2. Use a DMM to measure the resistance between terminal D of the heater and A/C control assembly connector C2 and ground.

Is the resistance measured within the specified range?

Infinite

Go to Step 12

Go to Step 13

12

Replace the heater and A/C control assembly. Refer to Control Assembly Replacement in HVAC Systems.

Is the repair complete?

--

Go to Defogger System Check

--

13

Repair the short to ground in CKT 193 between the heater and A/C control assembly and the underhood wiring harness junction block. Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Defogger System Check

--