Schematic Reference: Defogger Schematics

Connector End View Reference: Window Systems Connector End Views

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

Important: Make sure that system voltage is near normal operating range on the vehicle. This will effect the illumination of the rear window defogger indicator.

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 ground.

Does the test lamp illuminate?

Go to Step 4

Go to Step 8

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

Go to Step 14

5

Command the Rear Defog relay ON and OFF, by depressing the rear defogger switch on the HVAC control module.

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

Go to Step 12

Go to Step 6

1. Turn OFF the ignition.
2. Disconnect the Rear Defog relay.
3. Turn ON the ignition, with the engine OFF.
4. Connect a test lamp between the BATT main 3 fused voltage supply circuit of the Rear Defog relay coil and ground.

Does the test lamp illuminate?

Go to Step 7

Go to Step 15

1. Connect a test lamp between the BATT main 3 fused voltage supply 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 13

Go to Step 10

1. Turn OFF the ignition.
2. Disconnect the Rear Defog relay.
3. Connect a test lamp between the battery voltage circuit of the Rear Defog relay switched input and ground.

Does the test lamp illuminate?

Go to Step 9

Go to Step 16

1. Connect a 30-ampere fused jumper between the battery voltage circuit of the Rear Defog relay switched input and the relay switched output to the supply voltage circuit of the rear window defogger grid.
2. Connect a test lamp between the rear window defogger grid and a good ground.

Does the test lamp illuminate?

Go to Step 13

Go to Step 17

Test the control circuit of the Rear Defog relay for an open or short to ground. Refer to Circuit Testing and Wiring Repairs.

Did you find and correct the condition?

Go to Step 21

Go to Step 11

Inspect for a poor connection at the harness connector of the body control module (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

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.

Did you find and correct the condition?

Go to Step 21

Go to Step 18

Inspect for a poor connection 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 19

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

Did you find and correct the condition?

Go to Step 21

Go to Defogger Grid Lines Diagnosis

Repair an open or high resistance in the BATT main 3 fused voltage circuit of the Rear Defog relay coil. Refer to Wiring Repairs.

Did you complete the repair?

Go to Step 21

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Replace the I/P fuse block. Refer to Accessory Wiring Junction Block Replacement .

Did you complete the replacement?

Go to Step 21

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

Did you complete the repair?

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 Rear Defog relay. Refer to Relay Replacement.

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