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
--- | --- | --- | --- | ---
Relay Switch B+ | 1 | 1 | -- | --
Rear Defog Switch Signal | 2 | 1 | 1 | --
Rear Defog Relay Control | B0283 02 | B0283 05 | B0283 05 | --
Rear Window Defogger Grid Control | 1 | 1 | 2 | --
Rear Defog Indicator Control | B0283 02 | B0283 05 | B0283 05 | --
HVAC Ground | -- | 1 | 1 | --
Relay Coil Ground | -- | 1 | 1 | --
Rear Window Defogger Grid Ground | -- | 1 | 1 | --
1. Rear defogger Inoperative 2. Rear Defogger Always ON

### Circuit/System Description

Battery positive voltage is supplied through the REAR DEFOG fuse, in the underhood fuse block, to the REAR DEFOG relay switched input. The BCM supplies 12 volts on the rear window defogger switch signal circuit to the HVAC control assembly. When you depress the defog switch, the rear window defogger switch pulls the signal circuit low. The BCM interprets as a request for the rear window defogger system. The BCM enables the rear window defogger system by supplying voltage to the REAR DEFOG relay coil. The relay coil supply voltage is also spliced off internally in the BCM to the supply voltage circuit of the defogger indicator. The REAR DEFOG relay is energized and the defogger indicator is illuminated. With the relay energized, battery positive voltage is allowed from the relay switched input through the switch contacts and out the relay switched output to the rear window defogger grid.

### Conditions for Running the DTC

Battery voltage must be between 9-16 volts.

### Conditions for Setting the DTC

#### B0283 02

The BCM detects a short to ground in the relay coil control circuit or a short to ground in the defog indicator control circuit.

#### B0283 05

The BCM detects a concurrent short to voltage or an open/high resistance in both of the relay control and the rear defog indicator circuits.

### Action Taken When the DTC Sets

The rear window defogger will not operate.

### Conditions for Clearing the DTC

• | The DTC will be current for as long as the fault is present.

• | When the fault is no longer present, the DTC will be a history DTC.

• | A history DTC will clear after 50 ignition cycles.

### Reference Information

#### Schematic Reference

Defogger Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Rear Window Defogger Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

Ignition ON, command the Rear Defog Relay ON and OFF with a scan tool. The rear window defogger and rear window defogger indicator should turn ON and OFF when changing between the commanded states.

### Circuit/System Testing

1. Ignition OFF, disconnect the X2 harness connector at the HVAC control module.
2. Disconnect the REAR DEFOG relay.
3. Test for less than 1 ohm between the ground circuit terminal 86 and ground.

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

4. Connect a test lamp between the control circuit terminal 85 and ground circuit terminal 86.
5. Ignition ON, command the Rear 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.

6. Ignition OFF, connect the X2 harness connector at the HVAC control module.
7. Command the rear window defogger 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 does not turn ON and OFF, replace the HVAC control module.

8. If all circuits test normal, test or replace the REAR DEFOG relay.

### Component Testing

#### Relay Test

1. Ignition OFF, disconnect the REAR DEFOG relay.
2. Test for 60-180 ohms between terminals 85 and 86.

⇒ | If not within the specified range, replace the relay.

3. Test for infinite resistance between the following terminals:

• | 30 and 86

• | 30 and 87

• | 30 and 85

• | 85 and 87

⇒ | If not the specified value, replace the relay.

4. Install a 25-amp fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms between terminals 30 and 87.

⇒ | If greater than the specified range, replace the relay.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for BCM and HVAC replacement, setup and programming