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.
ONSTAR DTCS
's MPCS Unit (Door Switch Message) DTC B1406 OnStar Control Unit Lost Communication with Driver's MPCS Unit (Door Look Switch Message) DTC B1407 OnStar Control Unit Lost Communication with Driver's MPCS Unit (ASLOCKSW Message) DTC B1408 OnStar Control Unit Lost Communication with Gauge Control Module (VSP/NE Message) DTC B1425 OnStar Control Unit Lost Communication with SRS Unit (collision detection system line) DTC B1426 OnStar Switches Circuit Malfunction DTC B1427 Microphone Circuit Malfunction DTC B1428 GPS Antenna Circuit Malfunction DTC B1433 Cellular PHONE Antenna Circuit Malfunction
Use the Manual With the Right Hardware
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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.