Code P1811 is a diagnostic trouble code (DTC) that indicates an issue with the transmission range sensor circuit. This code is stored in the vehicle's on-board computer when it detects a problem with the input or output voltage of the transmission range sensor, which is responsible for monitoring and controlling gear selection. Common causes of this code include faulty wiring, connectors, or components related to the transmission range sensor such as a bad switch or solenoid valve. In some cases, this can be caused by a defective TCM (transmission control module). It’s important to diagnose and repair any issues associated with this diagnostic trouble code as soon as possible; otherwise it could lead to premature wear and tear of your vehicle’s transmission system. Fortunately, most modern vehicles are equipped with advanced diagnostics systems that allow technicians to accurately pinpoint and troubleshoot problems like these quickly and efficiently.