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

### Circuit/System Description

When the rear window defogger switch is pressed, the HVAC control module will energize the rear defog relay by providing a ground to the control circuit of the rear defog relay. This allows battery positive voltage from the relay switched input through the switch contacts and out the relay switched output to the rear window defogger grid. The HVAC control module contains the rear window defogger switch and also illuminates the rear defog indicator.

### Conditions for Running the DTC

Battery voltage must be between 9-16 volts.

### Conditions for Setting the DTC

#### B0283 02

The HVAC control module detects a short to ground in the relay control circuit.

#### B0283 05

The HVAC control module detects a short to voltage or an open/high resistance in the relay control circuit.

### Action Taken When the DTC Sets

• | If B0283 02 is current, the rear window defogger grid will operate continuously.

• | If B0283 05 is current, the rear window defogger grid will be inoperative.

### 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 ON and OFF with a scan tool. The E18 rear window defogger grid should turn ON and OFF when changing between the commanded states.

### Circuit/System Testing

1. Ignition OFF, disconnect the KR5 REAR DEFOG relay.
2. Test for less than 1 ohm between the ground circuit terminal 85 and ground.

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

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

⇒ | 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 HVAC control module.

5. If all circuits test normal, test or replace the KR5 REAR DEFOG relay.

### Component Testing

1. Ignition OFF, disconnect the KR5 REAR DEFOG relay.
2. Test for 60-180 ohms between terminals 85 and 86.

⇒ | If the not within the specified range, replace the KR5 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 KR5 relay.

4. Install a 25A fused jumper wire between relay terminal 85 and 12V. 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 KR5 relay.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Relay Replacement

• | Control Module References for HVAC control module replacement, setup and programming