Chevrolet Silverado / GMC Sierra. Service manual — part 2493

ground.

If the test lamp does not illuminate, replace the underhood fuse block.

4. Connect a test lamp between the relay control circuit terminal 85 and the B+ circuit

terminal 86.

5. Command the parking 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 relay control circuit for a short to ground. If the
circuit tests normal, replace the BCM.

If the test lamp is always OFF, test the relay control circuit for a short to voltage or an
open/high resistance. If the circuit tests normal, replace the BCM.

6. If all circuits test normal, test or replace the park lamp relay.

Exterior Lamps Circuit Test

1. Ignition OFF, disconnect the harness connector at an affected park, marker, license, or tail

lamp.

2. Verify that a test lamp illuminates when connected between battery voltage and the listed

ground circuit terminal.

Front park lamp terminal G

Tail lamp terminal GRD

Marker and clearance lamps terminal A

License lamp terminal B

If the test lamp does not illuminate, test the ground circuit for an open/high resistance.

3. Ignition ON, connect a test lamp between the listed control circuit terminal and ground.

Front park lamp terminal MAJ

Tail lamp terminal MNR

Marker and clearance lamps terminal B

License lamp terminal A

4. Command the parking 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 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.

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

2008 Chevrolet Silverado 1500

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

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Park/Turn Signal Lamp Bulb Replacement (Chevrolet) or Park/Turn Signal Lamp
Bulb Replacement (GMC)

Rear License Lamp Replacement (VF7) or Rear License Lamp Replacement
(Silverado)

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

Headlamp Switch Replacement (without RPO SLT) or Headlamp Switch
Replacement (with RPO SLT)

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

READING LAMPS MALFUNCTION

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.

Circuit/System Description

The inadvertent power supply voltage circuit of the body control module (BCM) provides battery
positive voltage to the reading lamps. The reading lamps and switch are integral to the
courtesy/reading lamp assembly. When the switch is closed, voltage is supplied and the lamp
illuminates.

Reference Information

Schematic Reference

Interior Lights Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Interior Lighting Systems Description and Operation

2008 Chevrolet Silverado 1500

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

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, turn the reading lamps on and off. The reading lamps should turn on and off.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at an affected courtesy/reading lamp center.

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

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

3. Ignition ON, verify that a test lamp illuminates between the listed inadvertent power supply

circuit terminal and ground.

Front terminal A

Rear terminal C

If the test lamp does not illuminate, test the inadvertent power supply circuit for a
short to ground or an open/high resistance. If the circuit tests normal replace the BCM.

4. Connect the harness connector at the courtesy/reading lamp center, and remove the reading

lamp bulb.

5. Connect a test lamp across the bulb terminals.

6. Ignition ON, turn the reading lamp switch on and off. The test lamp should turn on and off

when changing between the commanded states.

If the test lamp is always on, replace the affected courtesy/reading lamp center.

If the test lamp is always off, replace the affected courtesy/reading lamp center.

7. If all circuits test normal, test or replace the affected reading lamp bulb.

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

2008 Chevrolet Silverado 1500

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

Dome Lamp Replacement

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

STOP LAMPS MALFUNCTION

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.

Circuit/System Description

When the driver presses the brake pedal, the switch contacts open and battery positive voltage is
interrupted to the BCM. The BCM then supplies voltage to both the turn/stop lamp supply
voltage circuit and trailer rear turn/stop lamp supply voltage circuits. The BCM also supplies a
control voltage to the CHMSL relay energizing the relay and illuminating the CHMSL.

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

2008 Chevrolet Silverado 1500

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