Schematic Reference: Defogger Schematics

Connector End View Reference: Master Electrical Component List in Wiring Systems

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

1. Start the engine.
2. Depress the rear defogger switch.
3. Observe the rear defogger indicator on the HVAC control module.

Does the rear defogger indicator illuminate?

Go to Step 3

Go to Step 5

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

Does the test lamp illuminate?

Go to Step 4

Go to Step 8

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

Does the test lamp illuminate?

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

Go to Step 15

1. With a scan tool, observe the Rear Defog Switch parameter in the body control module (BCM) switch Input data list.
2. Depress the rear window defogger switch.

Does the scan tool display On?

Go to Step 7

Go to Step 6

1. Turn OFF the ignition.
2. Disconnect the harness C2 connector of the BCM.
3. Turn ON the ignition, with the engine OFF.
4. Connect a test lamp between battery voltage and the rear defogger switch signal circuit of the HVAC control module at the BCM.
5. Depress the rear defogger switch.

Does the test lamp illuminate?

Go to Step 13

Go to Step 10

Connect a test lamp between the defogger relay control circuit of the HVAC control module and battery positive voltage.

Does the test lamp illuminate?

Go to Step 12

Go to Step 14

8

1. With a scan tool select from the Special Functions, the Rear Defogger Relay under the BCM output controls.
2. Command the REAR DEFOG relay ON and OFF.

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

Go to Step 16

Go to Step 9

Connect a test lamp between the supply voltage circuit of the REAR DEFOG relay switched input, at the underhood fuse block, and a good ground.

Does the test lamp illuminate?

Go to Step 11

Go to Step 16

Test the rear defogger switch signal circuit and the rear defogger switch ground circuit of the HVAC control module for an open or short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 20

Go to Step 12

Inspect for poor connections at the REAR DEFOG 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 20

Go to Step 17

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 20

Go to Step 18

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 20

Go to Step 19

Repair an open or high resistance in the rear defogger relay control circuit between the instrument panel (I/P) fuse block and the HVAC control module. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 20

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

Did you complete the repair?

Go to Step 20

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Repair an open, a high resistance, or a short to ground in the supply circuit of the rear defogger. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 20

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Replace the REAR DEFOG relay. Refer to Relay Replacement in Wiring Systems.

Did you complete the replacement?

Go to Step 20

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Replace the HVAC control module. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 20

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Replace the BCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 20

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Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 2