Diagnostic Fault Information
Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Rear Defog Relay Control | B0283 02 | B0283 05 | B0283 05 | -- |
Rear Defog Switch Signal | 1 | 2 | -- | -- |
Rear Window Defogger Grid Voltage Supply | 2 | 2 | 1 | -- |
Rear Defog Indicator Voltage Supply | B0283 02 | B0283 05 | B0283 05 | -- |
Rear Defog Relay Voltage Supply | 2 | 2 | -- | -- |
Rear Defog Relay Ground | -- | 2 | 2 | -- |
Rear Window Defogger Grid Ground | -- | 2 | 2 | -- |
1. Defogger Always On - Rear Window 2. Defogger Inoperative - Rear Window | ||||
Circuit/System Description
The body control module (BCM) controls the rear window defog relay located in the underhood fuse block. The rear window defog switch located on the HVAC control module is hard wired to the BCM. The rear window defog switch provides the request signal to the BCM. With the ignition switch in the RUN position, the BCM supplies voltage to the rear window defog switch via the rear defog switch signal circuit. When the rear window defog switch is pressed, the switch contacts close and ground is supplied. The BCM interprets the flow of voltage as a request to turn the rear defogger ON. The BCM energizes the rear window defog relay by applying voltage to the relay coil via the rear defog relay control circuit. When the rear window defog relay coil is energized, the switch contacts of the rear window defog relay close allowing battery voltage to flow from the REAR DEFOG fuse through the closed switch contacts and out the relay switched output to the rear window defogger grid. Ground for the rear window defogger grid is provided at G301. The BCM also illuminates the rear defog indicator LED located on the HVAC control module with the supplied voltage from the rear defog relay control circuit.
Reference Information
Schematic Reference
Connector End View Reference
Stationary Windows Connector End Views
Electrical Information Reference
Scan Tool Reference
Circuit/System Testing
- Ignition OFF, disconnect the BCM C2 harness connector.
- Turn off the rear window defogger.
- Verify that a test lamp does not illuminate between battery voltage and the rear defog switch signal circuit at the BCM C2 harness connector.
- Disconnect the rear window defog relay.
- Ignition ON, verify that a test lamp does not illuminate between the rear defog relay control circuit and ground at the rear window defog relay terminals.
- Verify that a test lamp does not illuminate between the rear window defogger grid voltage supply circuit and ground at the rear window defog relay switched output terminal.
- If all circuits test normal, test or replace the rear window defog relay.
| ⇒ | If the test lamp illuminates, repair the rear defog switch signal circuit for a short to ground. If the circuit tests normal, replace the HVAC control module. |
| ⇒ | If the test lamp illuminates, repair the rear defog relay control circuit for a short to voltage. If the circuit tests normal, replace the BCM. |
| ⇒ | If the test lamp illuminates, repair the rear window defogger grid voltage supply circuit for a short to voltage. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for BCM and HVAC replacement, setup, and programming |
