GM Service Manual Online
For 1990-2009 cars only

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 Switch B+

2

2

--

--

Rear Defogger Relay Control

B0283 02

B0283 05

B0283 05

--

Rear Defogger Grid Control

2

2

1

--

Relay Coil Ground

--

B0283 05

2

--

Rear Window Defogger Grid Ground

--

2

2

--

1. Rear Defogger Always ON

2. Rear Defogger Inoperative

Circuit/System Description

The HVAC control module monitors the voltage level on the supply voltage circuit of the DEFOG relay. The voltage level should be low while the DEFOG relay is de-energized. The voltage will be near system voltage when the HVAC control module energizes the DEFOG relay.

Conditions for Running the DTC

Battery voltage must be between 9-16 volts.

Conditions for Setting the DTC

B0283 02

When the HVAC control module detects a short to ground in the rear defog relay control circuit for greater than 1 second.

B0286 05

When the HVAC control module detects a short to voltage or an open/high resistance in the rear defog relay control circuit or the rear defog relay ground circuit for greater than 1 second.

Action Taken When the DTC Sets

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

Circuit/System Testing

  1. Ignition OFF, disconnect the REAR DEFOG relay.
  2. Test for less than 1 ohm between the ground circuit terminal 85 and ground.
  3. If greater than the specified range, test ground circuit for an open/high resistance.
  4. Connect a test lamp between the control circuit terminal 86 and the ground circuit terminal 85.
  5. Ignition ON, command the Rear Defog Request ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
  6. 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.
  7. If all circuits test normal, test or replace the REAR DEFOG relay.

Component Testing

  1. Ignition OFF, disconnect the REAR DEFOG relay.
  2. Test for 60-180 ohms of resistance between terminals 85 and 86.
  3. If the resistance is not within the specified range, replace the relay.
  4. Test for infinite resistance between the following terminals:
  5. • 30 and 86
    • 30 and 87
    • 30 and 85
    • 85 and 87
    If not the specified value, replace the relay.
  6. 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 of resistance between terminals 30 and 87.
  7. If greater than the specified range, replace the 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