B1791: Autolamp Sensor Input Circuit Open
MediumBodyLighting
What does B1791 mean?
B1791 is a diagnostic trouble code indicating "Autolamp Sensor Input Circuit Open". This means there is an electrical break in the lighting wiring — a connector may be unplugged, a wire broken, or a component has failed internally. The ECU detected no signal where it expected one.
Common causes
- Damaged or corroded wiring harness
- Loose or disconnected electrical connector
- Failed lighting sensor or actuator
- Blown fuse in the related circuit
- Poor ground connection
What should you do?
Schedule a diagnostic appointment at your earliest convenience. The vehicle is generally safe to drive short distances, but the underlying issue should be addressed to prevent it from worsening.
Get a diagnosis for YOUR car
Code B1791 can mean different things depending on your vehicle. TorqueBot gives you a diagnosis specific to your make, model, and year.