Chevrolet Silverado / GMC Sierra. Service manual — part 2492

Driver window switch terminal A X2

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

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

Passenger window switch terminal B

Headlamp switch terminal 7

Transfer case control switch terminal 5

Sunroof switch terminal 3

Door lock switch terminal A

Roof beacon switch terminal 2

Sliding rear window switch terminal E

Garage door opener switch terminal 2

Outside rear view mirror switch terminal E

Driver window switch terminal 1 X1

4. Command the dimming test high to low with a scan tool. The test lamp should turn from

bright to dim when changing between the commanded states.

If the test lamp is always off, test the control circuit for an open/high resistance or
short to ground. If the circuit tests normal, replace the BCM.

If the test lamp is always bright, test the control circuit for a short to voltage. If the
circuit tests normal, replace the BCM.

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

LED Dimming Circuit Test

1. Ignition OFF, disconnect the harness connector at the affected component.

2. Ignition OFF, verify that a test lamp illuminates between the listed ground circuit terminal

and battery voltage.

Right steering wheel switch terminal 1

Left steering wheel switch terminal 8

DIC switch terminal 5

Manual HVAC control module terminal 10 X2

Multifunction accessory switch terminal 3

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

3. Connect a test lamp between the listed LED dimming control circuit terminal and ground.

Right steering wheel switch terminal 2

2008 Chevrolet Silverado 1500

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

Left steering wheel switch terminal 6

Power take off switch terminal 6

Trailer brake controller switch terminal 7

IPC terminal 8

Radio terminal 7 X1

DIC switch terminal 4

Manual HVAC control module terminal 1 X2

Multifunction accessory switch terminal 4

4. Command the dimming test high to low with a scan tool. The test lamp should turn from

bright to dim when changing between the commanded states.

If the test lamp is always off, test the control circuit for an open/high resistance or
short to ground. If the circuit tests normal, replace the BCM.

If the test lamp is always bright, test the control circuit for a short to voltage. If the
circuit tests normal, replace the BCM.

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

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Front Seat Heater Switch Replacement (w/o KB6)

Steering Wheel Control Switch Assembly Replacement

Driver Information Display Switch Replacement (without RPO SLT) or Driver
Information Display Switch Replacement (with RPO SLT)

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

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

Control Module References for BCM, IPC, radio, and HVAC control module
replacement, programming, and setup.

PARK, LICENSE, AND/OR TAIL 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.

2008 Chevrolet Silverado 1500

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

Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Circuit/System Description

The park, tail and marker lamps, including the license lamps, are turned ON when the headlamp
switch is placed in the PARK or HEAD position or anytime the headlights are requested. The
underhood fuse block supplies battery positive voltage to both the park lamp relay switch
contacts and the park lamp coil circuit. The BCM provides a ground or control circuit to the park
lamp relay coil circuit. When the park lamps are turned ON, the BCM energizes the park lamp
relay. If the headlight switch is left in the ON position, the inadvertent power control feature will
turn OFF the park, tail and marker lamps approximately 10 minutes after the ignition switch is
turned to the OFF position. If the driver places the headlight switch in the ON position after the
ignition switch has been turned OFF, or if the ignition switch is in the ACCY position, the park,
tail and marker lamps will remain ON until turned OFF or the battery runs dead.

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

2008 Chevrolet Silverado 1500

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

1. Ignition ON, observe the scan tool parklamp switch parameter while cycling the headlamp

switch between the park and off positions. The parameter should cycle between active and
inactive.

If the parameter does not cycle between the specified values, refer to Park Lamp
Switch Circuit Test below.

2. Connect a test lamp between the relay side of a park lamp fuse and ground.

3. Command the parking lamps on and off with a scan tool. Verify that the test lamp turns on

and off while switching between the commanded states.

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

4. If any of the park, marker, license, or tail lamps do not turn on and off, refer to the Exterior

Lamp Circuit Test below.

Circuit/System Testing

Park Lamp Switch Circuit Test

1. Ignition OFF, disconnect the harness connector at the headlamp switch.

2. Ignition OFF, test for less than 1.0 ohm of resistance between the ground circuit terminal 8

and ground.

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

3. Ignition ON, verify the scan tool parklamp switch parameter is inactive.

If not the specified value, test the signal circuit terminal 2 for a short to ground. If the
circuit tests normal, replace the BCM.

4. Install a 3A fused jumper wire between the signal circuit terminal 2 and ground. Verify the

scan tool BCM parklamp switch parameter is active.

If not the specified value, test the signal circuit for a short to voltage or open/high
resistance. If the circuit tests normal, replace the BCM.

5. If all circuits test normal, test or replace the headlamp switch.

Park Lamp Relay Circuit Test

1. Ignition OFF, disconnect the park lamp relay.

2. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal 30 and

ground.

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

3. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal 86 and

2008 Chevrolet Silverado 1500

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