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

Relay B+

B0283 05

B0283 05

--

--

Rear Defog Relay Control

B0283 02

B0283 05

B0283 05

--

Rear Defogger Grid Control

2

2

1

--

Rear Window Defogger Grid Ground

--

2

2

--

1. Rear defogger always On

2. Rear defogger inoperative

Circuit/System Description

When the rear defog switch is pressed, a signal is sent to the body control module (BCM) which energizes 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.

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.

B0283 05

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

Action Taken When the DTC Sets

B0283 02

The rear window defogger will operate continuously.

B0283 05

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 window defogger 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

Rear Defogger Malfunction

  1. Ignition OFF, disconnect the REAR/FOG relay.
  2. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal 85 and ground.
  3. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ curcuit fuse is open, test the control circuit terminal 87 for a short to ground.
  4. Connect a test lamp between the control circuit terminal 86 and the B+ circuit terminal 85.
  5. 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.
  6. If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the BCM.
    If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
  7. If all circuits test normal, test or replace the REAR/FOG relay.

Component Testing

Relay Test

  1. Ignition OFF, disconnect the REAR/FOG relay.
  2. Test for 60-180 ohms between terminals 85 and 86.
  3. If 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 greater than the specified range, replace the relay.
  6. Install a 40-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.
  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 BCM replacement, setup and programming