Chevrolet Silverado / GMC Sierra. Service manual — part 2483

Circuit/System Description

When the PRNDL is placed in the REVERSE position, a signal is sent to the body control
module (BCM). The BCM then applies voltage through the backup lamps relay control circuit to
the BACK/UP lamp relay in the underhood fuse block, and the inside rearview mirror. The
BACK/UP lamp relay then illuminates the backup lamps.

Reference Information

Schematic Reference

Exterior Lights Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Exterior Lighting Systems 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

1. Connect a test lamp between the relay side of the backup lamp fuse and ground.

Backup Lamp Relay Control

1

1

2

-

Backup Lamp Control

B2545 00

1

2

-

Backup Lamp Ground

-

1

-

-

1. Backup lamps inoperative
2. Backup lamps always on

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Lighting - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

2. Ignition ON, verify that the test lamp turns on and off while commanding the backup lamps

on and off with a scan tool.

If the test lamp does not turn on and off while changing between the commanded
states, refer to the Backup Lamp Relay Control Circuit Test below.

3. If 1 or both of the backup lamps do not turn on and off, refer to the Backup Lamp Circuit

Test below.

Circuit/System Testing

Backup Lamp Relay Control Circuit Test

1. Ignition OFF, disconnect the harness connector X5 at the BCM.

2. Ignition ON, vehicle in park, verify the backup lamps are not on.

If the backup lamps are on, test the backup lamp relay control circuit terminal11 for a
short to voltage. If the circuit tests normal replace the underhood fuse block.

3. Install a 10A fused jumper wire between the relay control circuit terminal 11 and battery

voltage. Verify the backup lamps are on.

If the backup lamps are not on, test the backup lamp relay control circuit for an
open/high resistance or short to gerund. If the circuit tests normal replace the
underhood fuse block.

4. If all circuits test normal, replace the BCM.

Backup Lamp Circuit Test

1. Ignition OFF, disconnect the harness connector at the affected backup lamp.

2. Test for less than 1 ohm of resistance between the ground circuit terminal GRD 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 MJR and the ground circuit

terminal GRD.

4. Command the backup lamps 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 underhood fuse block.

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 underhood fuse block.

5. If all circuits test normal, test or replace the affected backup lamp.

Repair Procedures

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Lighting - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Backup Lamp Bulb Replacement (GMC) or Backup Lamp Bulb Replacement
(Chevrolet)

Underhood Electrical Center or Junction Block Replacement

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

COURTESY LAMPS MALFUNCTION (W/AN3)

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.

Diagnostic Fault Information

Circuit/System Description

Voltage for the courtesy lamps is supplied from body control module (BCM), driver door switch,
and passenger door switch. When a door is opened, a signal is applied to the door module. The
door module then applies a message on the low speed GMLAN serial data communication circuit
to the BCM to activate the courtesy lamps. The BCM then applies voltage to the courtesy lamps
voltage supply circuit and the components on that circuit.

Reference Information

Circuit

Short to

Ground

Open/High

Resistance

Short to

Voltage

Signal

Performance

Dome Lamp Switch Signal

1

3

-

-

Interior Lamp Defeat Switch
Signal

2

4

-

-

Door Open Switch Signal

1

-

-

Courtesy Lamp Control

B2615

2

1

-

1. Courtesy lamps always on
2. Courtesy lamps inoperative
3. Courtesy lamps inoperative from dome lamp switch
4. Manual defeat switch inoperative
3. Courtesy lamps not on with door open

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Lighting - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

Schematic Reference

Interior Lights Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Interior Lighting Systems 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

1. Ignition ON, command the Courtesy Lamps output control on and off with the scan tool.

The interior courtesy lamps should turn on and off.

If one or more of the courtesy lamps are always on or always off refer to the courtesy
lamp control circuit test below.

2. Observe the scan tool Driver Door Switch, Driver Door Open Sw. parameter while opening

and closing the driver door. The reading should change between active and inactive.

If the Driver Door Open Sw. parameter does not change between active and inactive,
refer to Door Open Switch Test-Front below.

3. Observe the scan tool Passenger Door Switch, Passenger Door Open Sw. parameter while

opening and closing the front passenger door. The reading should change between active
and inactive.

If the Passenger Door Open Sw. parameter does not change between active and
inactive, refer to Door Open Switch Test-Front below.

4. Observe the scan tool BCM Ctsy. Lamp Actv. Reason parameter while opening and closing

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Lighting - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado