Chevrolet Silverado / GMC Sierra. Service manual — part 2475

The BCM receives a mismatched signal between the headlamp switch headlamps OFF signal
circuit, the headlamps switch headlamps ON signal circuit, and the headlamp switch parklamps
signal circuit.

Action Taken When the DTC Sets

The BCM disregards the headlamp switch input and defaults to automatic headlamp function.

Conditions for Clearing the DTC

The conditions for setting the DTC are no longer present.

A history DTC clears after 100 malfunction-free ignition cycles.

Reference Information

Schematic Reference

Headlights/Daytime Running Lights (DRL) 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

Ignition ON, headlamp switch to PARK, just the park lamps should illuminate. Headlamp switch
to HEAD, the park lamps and headlamps should illuminate.

2008 Chevrolet Silverado 1500

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

Circuit/System Testing

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

2. Ignition ON, verify the scan tool headlamp switch parameter is inactive.

If not the specified value, test the signal circuit terminal 1 for a short to ground. If the
circuit tests normal, replace the BCM.

3. Install a 3A fused jumper wire between the signal circuit terminal 2 and the low reference

circuit terminal 8. Verify the scan tool park lamp switch parameter is active.

If not the specified value, test the park lamp switch signal circuit for an open/high
resistance. If the circuit tests normal, replace the BCM.

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

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

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

Control Module References for BCM replacement, setup, and programming

DTC B2580

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

DTC B2580 00

Headlamp High Beam Control Circuit

Diagnostic Fault Information

Circuit

Short to

Ground

Open/High

Resistance

Short to

Voltage

Signal

Performance

Headlamp High Beam Relay
Control Circuit

2

1

B2580 00

-

2008 Chevrolet Silverado 1500

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

Circuit/System Description

Voltage is applied at all times to the high beam headlamp relay from battery voltage. When the
multifunction switch is placed in either the FTP or HIGH position, ground is applied to the body
control module (BCM). The BCM then applies a ground to the headlamp high beam relay control
circuit. This engages the relay and applies voltage through the HI HEADLAMP fuses to both left
and right high beam headlamps.

Conditions for Running the DTC

The headlamps are commanded ON.

Headlamp dimmer switch must be in the high beam position.

Conditions for Setting the DTC

The BCM detects a short to voltage on the headlamp high beam relay control circuit.

Action Taken When the DTC Sets

The high beam headlamps are inoperative.

Conditions for Clearing the DTC

The conditions for setting the DTC are no longer present.

A history DTC clears after 100 malfunction-free ignition cycles.

Reference Information

Schematic Reference

Headlights/Daytime Running Lights (DRL) Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Exterior Lighting Systems Description and Operation

1. Headlamps Inoperative - High Beams

2. Headlamps Always On - High Beams

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, activate the High Beam output control on the scan tool. The High Beam Relay
Command parameter in the data list should display On and the high beam headlamps should
illuminate.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector X4 at the BCM.

2. Low beam headlamps ON, verify the high beam headlamps are not on.

If the high beam headlamps are on, test the high beam relay control circuit for a short
to ground. If the circuit tests normal replace the underhood fuse block.

3. Install a 10A fused jumper wire between the relay control circuit terminal 16 and ground.

Verify the high beam headlamps are on.

If the high beam headlamps are not on, test the high beam relay control circuit for a
short to voltage or an open/high resistance. If the circuit tests normal replace the
underhood fuse block.

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

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Underhood Electrical Center or Junction Block Replacement

Control Module References for BCM replacement, setup, and programming

DTC B2585

Diagnostic Instructions

2008 Chevrolet Silverado 1500

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