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Chevrolet Silverado / GMC Sierra. 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
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