Schematic Reference: Defogger Schematics

Did you review the operation of the rear window defogger system and perform the necessary inspections?

Go to Step 2

Go to Symptoms - Stationary Windows

1. Turn ON the ignition, with the engine OFF.
2. Depress the rear window defogger switch.
3. Observe the rear window defogger indicator on the HVAC Control Module.

Does the rear window defogger indicator illuminate?

Go to Step 3

Go to Step 5

Connect a test lamp between the rear window defogger grid and a good ground.

Does the test lamp illuminate?

Go to Step 4

Go to Step 7

Connect a test lamp between the left side of the rear window defogger grid and the right side of the rear window defogger grid.

Does the test lamp illuminate?

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

Go to Step 16

1. Turn OFF the ignition.
2. Disconnect the harness connector of the HVAC Control Module.
3. Turn ON the ignition, with the engine OFF.
4. Connect a test lamp between the Ignition 3 voltage circuit of the HVAC Control Module and a good ground.

Does the test lamp illuminate?

Go to Step 6

Go to Step 17

Connect a test lamp between the Ignition 3 voltage circuit of the HVAC control module and the ground circuit of the HVAC control module.

Does the test lamp illuminate?

Go to Step 14

Go to Step 18

7

Command the Rear Window Defogger relay ON and OFF, by depressing the rear window defogger switch on the HVAC Control Module.

Do you hear a click when you command the Rear Window Defogger relay ON and OFF?

Go to Step 10

Go to Step 8

1. Turn OFF the ignition.
2. Disconnect the Rear Window Defogger relay.
3. Turn ON the ignition, with the engine OFF.
4. Connect a test lamp between the Ignition 1 voltage circuit of the Rear Window Defogger relay coil and a good ground.

Does the test lamp illuminate?

Go to Step 9

Go to Step 19

1. Connect a test lamp between the Ignition 1 voltage circuit of the Rear Window Defogger relay coil and the control circuit of the Rear Window Defogger relay.
2. Depress the rear window defogger switch.

Does the test lamp illuminate?

Go to Step 15

Go to Step 12

1. Turn OFF the ignition.
2. Disconnect the Rear Window Defogger relay.
3. Connect a test lamp between the battery positive voltage circuit of the Rear Window Defogger relay switch and a good ground.

Does the test lamp illuminate?

Go to Step 11

Go to Step 13

1. Connect a 30 amp fused jumper wire between the battery positive voltage circuit of the Rear Window Defogger relay switch and the supply voltage circuit of the rear window defogger.
2. Connect a test lamp between the rear window defogger grid and a good ground.

Does the test lamp illuminate?

Go to Step 15

Go to Step 21

Test the control circuit of the Rear Window Defogger relay for an open or short to battery positive voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 24

Go to Step 14

Test the battery positive circuit of the Rear Window Defogger relay switch for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 24

Go to Step 20

Inspect for a poor connection at the harness connector of the HVAC Control Module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 24

Go to Step 22

Inspect for a poor connection at the Rear Window Defogger relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 24

Go to Step 23

Repair an open or high resistance in the ground circuit of the rear window defogger grid. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 24

--

Repair an open or short to ground in the Ignition 3 voltage circuit of the HVAC Control Module. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 24

--

Repair an open or high resistance in the ground circuit of the HVAC Control Module. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 24

--

Repair an open or high resistance in the Ignition 1 voltage circuit of the Rear Window Defogger relay coil. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 24

--

Repair the short to ground in the supply voltage circuit of the rear window defogger. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 24

--

Repair an open or high resistance in the supply voltage circuit of the rear window defogger. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 24

--

Replace the HVAC Control Module. Refer to Heater and Air Conditioning Control Replacement in HVAC Systems - Manual or HVAC Control Module Replacement in HVAC Systems - Automatic.

Did you complete the replacement?

Go to Step 24

--

Replace the Rear Window Defogger relay.

Did you complete the replacement?

Go to Step 24

--

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 2