Schematic Reference: Defogger Schematics

Connector End View Reference: Master Electrical Component List

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

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 supply voltage side of 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

Go to Step 17

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 that contains the rear defogger switch signal circuit 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 at the BCM connector.
5. Depress the rear defogger switch.

Does the test lamp illuminate?

Go to Step 16

Go to Step 10

1. Connect a test lamp between the defogger relay control circuit and ground.
2. Depress the rear window defogger switch.

Does the test lamp illuminate?

Go to Step 13

Go to Step 11

8

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

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

Go to Step 12

Go to Step 9

Connect a test lamp between the supply voltage circuit of the rear defog relay switched input and a good ground.

Does the test lamp illuminate?

Go to Step 11

Go to Step 12

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 .

Did you find and correct the condition?

Go to Step 20

Go to Step 12

Test for an open or high resistance in the rear defogger relay control circuit and ground circuit. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 21

Go to Step 16

Test the supply voltage circuit for the following conditions:

Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 21

Go to Step 13

Test for the following in the rear defogger indicator supply voltage circuit:

Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 21

Go to Step 15

Inspect for poor connections at the rear defog relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 21

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 .

Did you find and correct the condition?

Go to Step 21

Go to Step 19

Inspect for poor connections at the harness connector of the BCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 21

Go to Step 20

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

Did you complete the repair?

Go to Step 21

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Replace the rear defog relay. Refer to Relay Replacement .

Did you complete the replacement?

Go to Step 21

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Replace the HVAC control module. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 21

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Replace the BCM. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 21

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Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 2