For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using the diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptor

DTC B0283 02: Electric Rear Defrost Circuit Short to Ground
DTC B0283 05: Electric Rear Defrost Circuit Short to Battery or Open

### Diagnostic Fault Information

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.

### Conditions for Running the DTC

Battery voltage must be between 9-16 volts.

### Conditions for Setting the DTC

#### C0283 02

This DTC will set when the BCM detects a short to ground in the rear defog relay control circuit or rear defog indicator voltage supply circuit for 1 second or greater.

#### C0283 05

This DTC will set when the BCM detects a short to voltage or an open in the rear defog relay control circuit or rear defog indicator voltage supply circuit for 1 second or greater.

### Action Taken When the DTC Sets

• | The BCM stores the DTC to memory.

• | The rear window defogger will not operate.

### Conditions for Clearing the DTC

• | The condition responsible for setting the DTC no longer exists.

• | You issue a scan tool CLEAR DTCs command.

• | A history DTC will clear once 100 malfunction-free ignition cycles have occurred.

### Reference Information

#### Schematic Reference

Defogger Schematics

#### Connector End View Reference

Window Systems Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

• | Scan Tool Data Definitions

• | Scan Tool Data List

• | Scan Tool Output Controls

### Circuit/System Testing

#### B0283 02

1. Ignition OFF, disconnect the rear window defog relay.
2. Connect a test lamp between the rear defog relay control circuit at the rear window defog relay terminal and ground.
3. Ignition ON, with a scan tool, command the rear window defog relay on and off, the test lamp should turn ON and OFF with each scan tool command.

⇒ | If the test lamp does not turn ON and OFF with each scan tool command, test for a short to ground in the rear defog relay control circuit or the rear defog indicator voltage supply circuit. If the circuits test normal, replace the BCM.

4. If all circuits test normal, test or replace the rear window defog relay.

#### B0283 05

1. Ignition OFF, disconnect the rear window defog relay.
2. Verify that a test lamp illuminates between battery voltage and the rear defog relay coil side ground circuit at the rear window defog relay terminal.

⇒ | If the test lamp does not illuminate, repair the rear defog relay coil side ground circuit for an open/high resistance.

3. Ignition ON, turn off the rear window defogger.
4. Verify that a test lamp between the rear defog relay control circuit at the rear window defog relay terminal and ground does not illuminate.

⇒ | If the test lamp illuminates, repair the rear defog relay control circuit or the rear defog indicator voltage supply circuit for a short to voltage. If the circuits test normal, replace the BCM.

5. Turn the rear window defogger on, the test lamp should illuminate.

⇒ | If the test lamp does not illuminate, repair the rear defog relay control circuit or the rear defog indicator voltage supply circuit for an open/high resistance. If the circuits test normal, replace the BCM.

6. If all circuits test normal, test or replace the rear window defog relay.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Control Module References for BCM replacement, setup, and programming.

• | Relay Replacement