What does it mean?
P1811 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Input/Turbine Speed Sensor Circuit Malfunction Lower Threshold .
Symptoms
- Check engine lamp on, often together with other transmission codes
- Transmission stays in one gear or shifts only at very high engine speed
- Delayed or slipping engagement when pulling away
- Torque converter clutch never locks up, so cruising rpm is high and fuel use climbs
- Limp mode with a firm, single-gear feel and poor drivability
Likely causes
- Open circuit in the signal or sensor ground wire, frequently at the transmission case connector
- Signal wire shorted to ground against the case, a heat shield or a chafed loom clip
- Water or automatic transmission fluid inside the connector corroding the pins and adding resistance
- Sensor mounted loose or with too large an air gap after a repair, weakening the pulse amplitude
- Worn, oil-caked or broken teeth on the tone ring the sensor reads
- Internally open sensor winding, sometimes only when cold
- Damaged input stage in the module after a long-standing short to ground
How to fix it
- Read the codes and freeze frame, then note whether the fault appears cold, hot or only above a certain road speed
- Inspect the harness from the case connector to the module for chafe points, crushed sections and repair splices
- Check the connector for fluid, corrosion and loose terminals; drag-test each terminal with a matching pin
- Measure sensor resistance against specification, then check the signal and ground wires for continuity and shorts to ground
- With the wheels safely off the ground, watch the input speed value on the scan tool while the transmission turns; a flat zero confirms a lost signal
- Remove and inspect the sensor tip and tone ring, and verify the sensor seats fully
- Replace the sensor or repair the harness as the tests dictate, then confirm the reading tracks engine rpm on a road test