Chevrolet Silverado / GMC Sierra. Service manual — part 2479

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

Ignition ON, headlamp switch to PARK, vary the interior lamp dimming switch from dim to full
bright. The LED lamps should dim and then become full bright.

Circuit/System Testing

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

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

IP multifunction switch terminal 6

4wd mode switch terminal 4

PTO switch terminal 7

3. 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.

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

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

Refer to the appropriate replacement procedure for the component causing the condition.

Control Module References for BCM replacement, setup, and programming

DTC B2645

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 B2645 03

Ambient Light Sensor Circuit Below Threshold

DTC B2645 07

Ambient Light Sensor Circuit Above Threshold

Diagnostic Fault Information

Circuit/System Description

The ambient light sensor is used to monitor outside lighting conditions. The ambient light sensor
provides a voltage signal that will vary depending on outside lighting conditions. The body
control module (BCM) provides a 5-volt reference signal to the ambient light sensor. The BCM
monitors the ambient light sensor signal circuit to determine if outside lighting conditions are
correct for either daytime running lights (DRL) or automatic lamp control (ALC) when the
headlamp switch is in the AUTO position. In daylight conditions, the BCM will command the
DRLs ON. In low light conditions, when the headlamps switch is in AUTO position, the BCM
will command the low beam headlamps ON.

Circuit

Short to

Ground

Open/High

Resistance

Short to

Voltage

Signal

Performance

Ambient Light Sensor Signal
Circuit

B2645 03

B2645 07

B2645 07

B2645 03 or

B2645 07

Ambient Light Sensor Ground
Circuit

-

B2645 07

-

B2645 03 or

B2645 07

2008 Chevrolet Silverado 1500

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

Conditions for Running the DTC

Battery voltage must be between 9-16 volts.

Conditions for Setting the DTC

B2645 03

The DTC will set when the BCM detects voltage is below 0.196 volt in the ambient light sensor
signal circuit.

B2645 07

The DTC will set when the BCM detects voltage is above 4.9 volts in the ambient light sensor
signal circuit or if the ambient light sensor ground circuit is open.

Action Taken When the DTC Sets

When DTC B2645 03 or B2645 07 is present, the ALC will default to ON.

Conditions for Clearing the DTC

The condition responsible for setting the DTC no longer exists.

A history DTC will clear once 100 consecutive malfunction-free ignition cycles have
occurred.

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

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Lighting - 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 Testing

1. Ignition OFF, disconnect the harness connector at the ambient light sensor.

2. Ignition OFF, test for less than 1 ohm of resistance between the ground circuit terminal C

and ground.

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

3. Ignition ON, verify the scan tool ambient light sensor parameter is greater than 4.5 volts.

If less than the specified range, test the signal circuit 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 D and the low reference

circuit terminal C. Verify the scan tool light sensor parameter is less than 1.0 volt.

If greater than the specified range, test the signal 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 ambient light sensor.

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Ambient Light Sensor Replacement

Control Module References for BCM replacement, setup, and programming

DTC B2652

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 Descriptor

2008 Chevrolet Silverado 1500

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