Chevrolet Silverado / GMC Sierra. Service manual — part 2490

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

Ignition ON, low beam headlamps ON, turn the headlamp dimmer switch to the high beam
position and observe the headlamps and the IPC high beam indicator. The high beam headlamps
and the high beam indicator should illuminate.

Circuit/System Testing

Ignition ON, with a scan tool perform the Display Test for the instrument panel cluster (IPC) and
observe the high beam indicator.

If the high beam indicator does not illuminate during the test or remains illuminated at all
times, replace the IPC.

If the high beam indicator illuminates during the test, replace the BCM.

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

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

INTERIOR BACKLIGHTING 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.

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

When the ignition switch is turned to the RUN position, the radio VF display turns ON at
maximum brightness. When the park lamps are ON, all incandescent and LED back lighting turn
ON at the dimming level indicated by the instrument panel (I/P) dimmer switch. At the same time
all VF displays dim to match the indicated dimming level. The panel dimmer switch
potentiometer is an input to the body control module (BCM). When the driver selects a dimming
setting by moving the I/P dimming switch potentiometer, all incandescent back lighting lamps are
provided with a specific voltage. When the I/P dimmer switch is moved from MIN to MAX, all
VF displays, as well as all incandescent back lighting respond from minimum intensity to
maximum brightness in response to the I/P dimmer switch

Reference Information

Schematic Reference

Interior Lights Dimming 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

2008 Chevrolet Silverado 1500

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

1. Ignition ON, observe the driver door switch while commanding the Driver Door Switch

Integrated Sw. Backlighting Test ON and OFF with a scan tool. The switch backlighting
should turn ON and OFF between commanded states.

If the backlighting does not turn On and OFF or remains always ON, replace the
driver door lock and side window switch.

2. Ignition ON, observe the driver memory/heated seat switch while commanding the Driver

Door Switch Non-Integrated Sw. Backlighting Test ON and OFF with a scan tool. The
switch backlighting should turn ON and OFF between commanded states.

If the backlighting does not turn On and OFF or remains always ON, refer to Front
Door Switch Backlighting Circuit Test below.

3. Ignition ON, observe the passenger door switch while commanding the Passenger Door

Switch Integrated Sw. Backlighting Test ON and OFF with a scan tool. The switch
backlighting should turn ON and OFF between commanded states.

If the backlighting does not turn On and OFF or always remains ON, replace the
passenger door lock and side window switch.

4. Ignition ON, observe the passenger heated seat switch while commanding the Passenger

Door Switch Non-Integrated Sw. Backlighting Test ON and OFF with a scan tool. The
switch backlighting should turn ON and OFF between commanded states.

If the backlighting does not turn On and OFF or remains always ON, refer to Front
Door Switch Backlighting Circuit Test below.

5. Ignition ON, observe the scan tool BCM Dimming Control Signal parameter while

operating the dimmer switch from high to low. The reading should change from a high
percent to a low percent as the switch is rotated.

If the reading does not change, refer to Dimmer Switch Circuit Test below.

If the scan tool dimmer control operates normal, refer to the Interior Backlighting Circuit
Test or the LED Dimming Circuit Test below.

Circuit/System Testing

Dimmer Switch Circuit Test

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

2. Ignition OFF, verify that a test lamp illuminates between the ground circuit terminal 8 and

B+.

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

3. Ignition ON, verify the scan tool Dimming Control Signal parameter is less than 0.1 volts.

2008 Chevrolet Silverado 1500

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

If greater than the specified range, test the signal circuit terminal 13 for a short to
voltage. If the circuit tests normal, replace the BCM.

4. Ignition ON, test for B+ between the I/P dimming voltage reference circuit terminal 15 and

ground.

If less than the specified value, test the voltage reference circuit for a short to ground
or an open/high resistance. If the circuit tests normal, replace the BCM.

5. Install a 3A fused jumper wire between the signal circuit terminal 13 and the voltage

reference circuit terminal 15. Verify the scan tool BCM Dimming Control Signal parameter
is greater than 2.6 volts.

If less than the specified range, test the signal circuit for a short to ground or an
open/high resistance. If the circuit tests normal, replace the BCM.

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

Interior Backlighting 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.

Rear window switch terminal F

Headlamp switch terminal 8

Transfer case control switch terminal 6

Sunroof switch terminal 5

Roof beacon switch terminal 1

Sliding rear window switch terminal D

Garage door opener 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 backlighting control circuit terminal and ground.

Rear window switch terminal B

Headlamp switch terminal 7

Transfer case control switch terminal 5

Sunroof switch terminal 3

Roof beacon switch terminal 2

Sliding rear window switch terminal E

Garage door opener switch terminal 2

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

2008 Chevrolet Silverado 1500

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