For 1990-2009 cars

### Diagnostic Instructions

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

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

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

### DTC Descriptors

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, 1 | B0283 05, 1 | B0283 05, 1 | --
Rear Defog Switch Signal | 1 | 1 | -- | --
Rear Defog Relay Switch B+ | 1 | 1 | 1 | --
Rear Defog Relay Switch Control | 1 | 1 | -- | --
Rear Defog Relay Coil Ground | -- | 1 | 1 | --
Rear Window Defogger Grid Ground | -- | 1 | 1 | --
1. Rear Window Defogger Malfunction

### 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 circuits 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 circuits 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

1. Ignition OFF, disconnect the rear window defog relay.
2. Test for less than 1.0 ohm of resistance between the rear defog relay coil side ground circuit and ground.

⇒ | If greater than the specified range, test the ground circuit for an open/high resistance.

3. Connect a test lamp between the rear defog relay control circuit and ground.
4. Command the rear window defog relay ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

⇒ | If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the BCM.

⇒ | If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.

5. 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.

• | Underhood Electrical Center or Junction Block Replacement

• | Relay Replacement

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