Chevrolet Silverado / GMC Sierra. Service manual — part 2960

DIAGNOSTIC STARTING POINT - FIXED AND MOVEABLE WINDOWS

Begin the system diagnosis with the Diagnostic System Check - Vehicle . The Diagnostic
System Check will provide the following information:

The identification of the control modules which command the system.

The ability of the control modules to communicate through the serial data circuit.

The identification of any stored diagnostic trouble codes (DTCs) and their status.

The use of the Diagnostic System Check will identify the correct procedure for diagnosing the
system and where the procedure is located.

DTC B0283

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 06

Electric Rear Defrost Circuit Short To Ground or Open

Diagnostic Fault Information

Circuit/System Description

Circuit

Short to

Ground

Open/High

Resistance

Short to

Voltage

Signal

Performance

Relay Switch B+

2

2

-

-

Rear Defog Relay Control

B0283 06

B0283 06

2

-

Rear Defog Relay Ground

-

B0283 06

2

-

Rear Defogger Control

2

2

1

-

Rear Window Defogger Grid
Ground

-

2

2

-

1. Rear Defogger Always On
2. Rear Defogger Inoperative

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Fixed and Moveable Windows - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado

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

Conditions for Running the DTC

Battery voltage must be between 9-16 volts.

Conditions for Setting the DTC

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

Action Taken When the DTC Sets

The HVAC control module stores the DTC to memory.

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

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Fixed and Moveable Windows - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado

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, observe the operation of the defogger grid while pressing and depressing the rear
defogger switch. The defogger grid should ACTIVATE and DEACTIVATE when changing
between commanded states.

Circuit/System Testing

1. Ignition OFF, disconnect the REAR DEFOG relay.

2. Test for less than 1.0 ohm between the ground circuit terminal 85 and ground.

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

3. Connect a test lamp between the control circuit terminal 86 and ground.

4. Ignition ON, command the defogger grid ON and OFF by pressing and depressing the rear

defogger switch. 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 REAR DEFOG relay.

Component Testing

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

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Fixed and Moveable Windows - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado

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 Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Relay Replacement (Attached to Wire Harness) or Relay Replacement (Within an
Electrical Center)

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

DTC B3205

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 B3205 00

Window Inactive Over Current Fault

DTC B3205 0B

Window Motor Fast Over Current Fault

Diagnostic Fault Information

Circuit

Short to

Ground

Open/High

Resistance

Short to

Voltage

Signal

Performance

Driver Door Switch B+

1, 3

1

-

-

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Fixed and Moveable Windows - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado