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 MANUALSCHEVROLET2006SUBURBAN C2500, 6.0 UREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 1220 (LIGHTING SYSTEMS)DIAGNOSTIC INFORMATION AND PROCEDURESDTC B257ACIRCUIT/SYSTEM TESTING
2006 Chevrolet Suburban C2500, 6.0 U
Circuit/System Testing
2006 Chevrolet Suburban C2500, 6.0 USECTION Circuit/System Testing
WARNING: This page is about a different car, the 2008 Cadillac CTS. However, it is still accessible from the selected car via links, so may be relevant.
- Ignition OFF, disconnect the X1 and X2 harness connectors at the BCM.
- Connect a test lamp between the headlamp switch OFF signal circuit terminal 23 and B+.
- 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 test normal, replace the turn signal/multifunction switch.
- If the test lamp is always ON, test the signal circuit for a short to ground. If the circuit test normal, replace the turn signal/multifunction switch.
- Connect a test lamp between the headlamp switch headlamps ON signal circuit terminal 12 and B+.
- 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 test normal, replace the turn signal/multifunction switch.
- If the test lamp is always ON, test the signal circuit for a short to ground. If the circuit test normal, replace the turn signal/multifunction switch.
- Connect a test lamp between the park lamp switch ON signal circuit terminal 8 and B+.
- Turn the headlamp switch to the PARK 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 test normal, replace the turn signal/multifunction switch.
- If the test lamp is always ON, test the signal circuit for a short to ground. If the circuit test normal, replace the turn signal/multifunction 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.