What does it mean?
P1816 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: A/T Input Shaft Speed Sensor Malfunction (4T40-E/4T45-E) .
Symptoms
- Check engine lamp on with a transmission fault message on some clusters
- Shift quality varies from soft and slipping to sharp and abrupt
- Torque converter clutch cycles in and out or never engages
- The unit locks into a fixed gear as a protective measure
- Higher cruising rpm, increased fuel use and reduced drivability
Likely causes
- Sensor internally failed, typically open or drifting once the fluid warms up
- Fluid intrusion or corrosion in the sensor connector adding resistance to the signal path
- Chafed or pinched wiring between the sensor and the module, often at the case pass-through
- Loose sensor mounting, missing shim or a distorted mounting boss opening the air gap
- Debris or clutch material stuck to the sensor tip after internal wear
- Damaged reluctor teeth on the input drum, sometimes following a hard failure inside the unit
- Module input circuit damaged by a previous short
How to fix it
- Retrieve all codes and freeze frame data, then note the fluid temperature at which the fault occurs
- Check the fluid level and condition, since burnt or debris-laden fluid points to internal wear behind the sensor complaint
- Inspect the connector and harness for fluid, corrosion, chafe and repair splices
- Measure sensor resistance and supply, then graph input speed against engine rpm during a road test
- Remove the sensor and inspect the tip, the air gap and the reluctor teeth
- Replace the sensor once the wiring proves good, then clear codes and repeat the drive cycle
- If the signal stays erratic with a new sensor and sound wiring, investigate the input drum and the internal harness