Schematic Reference: Defogger Schematics

Did you perform the Defogger Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - Defogger

1. Start the engine.
2. Operate the HVAC controls on the HVAC Control Module.

Does the HVAC system operate normally?

Go to Step 3

Go to Diagnostic System Check - HVAC Systems - Automatic in HVAC Systems - Automatic

1. Depress the rear window defogger switch.
2. Observe the rear window defogger indicator on the HVAC Control Module.

Does the rear window defogger indicator illuminate?

Go to Step 4

Go to Step 13

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

Does the test lamp illuminate?

Go to Step 5

Go to Step 6

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

6

1. Select from the special functions, the Rear Defogger from the Body Control Module (BCM) miscellaneous test, under output controls.
2. With a scan tool, command the REAR DEFOGGER relay ON and OFF.

Do you hear a click when you command the REAR DEFOGGER relay ON and OFF?

Go to Step 9

Go to Step 7

1. Turn OFF the ignition.
2. Disconnect the REAR DEFOGGER relay.
3. Turn ON the ignition, with the engine OFF.
4. Connect a test lamp between the Off/Run voltage circuit of the REAR DEFOGGER relay coil and a good ground.

Does the test lamp illuminate?

Go to Step 8

Go to Step 17

1. Connect a test lamp between the control circuit of the REAR DEFOGGER relay and the Off/Run voltage circuit of the REAR DEFOGGER relay coil.
2. With a scan tool, command the REAR DEFOGGER relay ON.

Does the test lamp illuminate?

Go to Step 14

Go to Step 11

1. Turn OFF the ignition.
2. Disconnect the REAR DEFOGGER relay.
3. Turn ON the ignition, with the engine OFF.
4. Connect a test lamp between the battery positive voltage circuit of the REAR DEFOGGER relay switch and a good ground.

Does the test lamp illuminate?

Go to Step 10

Go to Step 12

1. Connect a 40 amp fused jumper between the battery positive voltage circuit of the REAR 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 14

Go to Step 18

Test the control circuit of the REAR 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 22

Go to Step 15

Test the battery positive voltage circuit of the REAR 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 22

Go to Step 18

Inspect for poor connections 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 22

Go to Step 19

Inspect for poor connections at the REAR 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 22

Go to Step 20

Inspect for poor connections at the harness connector of the BCM. 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 22

Go to Step 21

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

Did you find and correct the condition?

Go to Step 22

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Repair an open or a short to ground in the Off/Run voltage circuit of the REAR DEFOGGER relay coil. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 22

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

Did you find and correct the condition?

Go to Step 22

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Replace the HVAC Control Module. Refer to HVAC Control Module Replacement in HVAC System - Automatic.

Did you complete the replacement?

Go to Step 22

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Replace the REAR DEFOGGER relay.

Did you complete the replacement?

Go to Step 22

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Important: Perform the setup procedure for the Body Control Module (BCM).

Replace the Body Control Module (BCM). Refer to Body Control Module Replacement in Body Control System.

Did you complete the replacement?

Go to Step 22

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Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 2