Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCHEVROLET2008CHEVY EXPRESS G2500, VAN CARGO, 6.6 6REPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 1607 (LIGHTING SYSTEMS)DIAGNOSTIC INFORMATION AND PROCEDURESDTC B257ACIRCUIT/SYSTEM TESTING
2008 Chevrolet Chevy Express G2500, Van Cargo, 6.6 6
Circuit/System Testing
2008 Chevrolet Chevy Express G2500, Van Cargo, 6.6 6SECTION Circuit/System Testing
WARNING: This page is about a different car, the 2009 GMC Sierra, 2009 GMC Cab & Chassis Sierra, 2009 Chevrolet Silverado, and 2009 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
- Ignition OFF, disconnect the X2 harness connector at the BCM.
- Connect a test lamp between B+ and the signal circuit terminal 17.
- Turn the headlamp switch between the headlamp AUTO and headlamp OFF positions. The test lamp should turn ON and OFF as the switch is cycled.
- If the test lamp is always OFF, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the headlamp switch.
- If the test lamp is always ON, test the signal circuit for a short to ground. If the circuit tests normal, replace the headlamp switch.
- Connect a test lamp between B+ and the signal circuit terminal 12.
- Turn the headlamp switch to the ON and OFF positions. The test lamp should turn ON and OFF as the switch is cycled.
- If the test lamp is always OFF, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the headlamp switch.
- If the test lamp is always ON, test the signal circuit for a short to ground. If the circuit tests normal, replace the headlamp switch.
- If all circuits test normal, replace the BCM.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.