Chevrolet Silverado / GMC Sierra. Service manual — part 2474

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Testing

1. Disconnect the X2 harness connector at the affected door module.

2. Verify that a test lamp illuminates between the ground circuit terminal 15 and B+.

If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
If the circuit tests normal replace the affected door module.

3. Connect a test lamp between the control circuit terminal 10 and the ground circuit terminal

15.

4. Command the Puddle/Courtesy Lamp 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 voltage. If the
circuit tests normal, replace the affected door module.

If the test lamp is always OFF, test the control circuit for a short to ground or an
open/high resistance. If the circuit tests normal, replace the affected door module.

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

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for driver or passenger door lock and side window switch
replacement, setup, and programming

DTC B2575

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 2575 00

Headlamp Control Circuit

2008 Chevrolet Silverado 1500

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

Diagnostic Fault Information

Circuit/System Description

The low beam headlamps are controlled by the body control module (BCM). The BCM grounds
the headlamp low beam relay control circuit in order to energize the LO BEAM relay coil. The
LO BEAM relay then sends voltage to the low beam headlamps.

Conditions for Running the DTCs

The headlamps are commanded ON.

The headlamp dimmer switch must be in the low beam position.

Condition for Setting the DTC

The headlamp low beam relay control circuit is shorted to voltage.

Action Taken When the DTC Sets

The BCM turns off the headlamp low beam relay control for the remainder of the ignition cycle.

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

Circuit

Short to

Ground

Open/High

Resistance

Short to

Voltage

Signal

Performance

Headlamp Low Beam Relay
Control Circuit

2

1

B2575 00

-

1. Headlamps Inoperative - Low Beams

2. Headlamps Always On - Low Beams

2008 Chevrolet Silverado 1500

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

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

Circuit/System Testing

1. Ignition OFF, remove the low beam relay in the underhood fuse block.

2. Ignition ON, test for voltage at the relay control circuit terminal 85 of the underhood fuse

block.

If voltage is present, test the control circuit for a short to voltage. If the circuit tests
normal, replace the underhood fuse block.

If voltage is not present, replace the BCM.

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Relay Replacement (Attached to Wire Harness) or Relay Replacement (Within an
Electrical Center)

Control Module References for BCM replacement, setup, and programming

DTC B257A

2008 Chevrolet Silverado 1500

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

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 B257A 00

Headlamp Switch Input Signal Mismatch

Diagnostic Fault Information

Circuit/System Description

When the headlamp switch is in the AUTO position, the body control module (BCM) receives a
ground signal through the headlamp switch headlamps OFF signal circuit and no signal on the
headlamp switch headlamp ON signal circuit and headlamp switch park lamps ON signal circuit.
When the headlamp switch is in the PARK or HEAD position, the BCM receives no signal
through the headlamp switch headlamps OFF signal circuit and a ground signal through the
headlamp switch headlamp ON signal circuit and headlamp switch park lamps ON signal circuit.

Conditions for Running the DTC

The ignition is ON.

Conditions for Setting the DTC

Circuit

Short to

Ground

Open/High

Resistance

Short to

Voltage

Signal

Performance

Headlamp Switch Off

B257A 00

2 and 4

4

-

Park Lamp Switch On

B257A 00

B257A 00

3

-

Headlamp Switch On

B257A 00

1

1

-

Headlamp Switch Ground

-

1,3, and 4

-

-

1. Headlamps Inoperative Low and High Beams

2. Headlamps Always On Low or High Beam

3. Park, License, and Tail Lamps Inoperative

4. Daytime Running Lamps (DRL) Defeat Inoperative

2008 Chevrolet Silverado 1500

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