What does it mean?
P1861 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Throttle Position Sensor Message from ECM .
Symptoms
- Check engine lamp on, normally with throttle-related codes stored as well
- Shift points wrong, with the transmission shifting far too early or too late
- No kick down when the pedal is pushed to the floor
- Harsh shifts or a delayed response to throttle input
- Limp mode, reduced power and clearly worse drivability
Likely causes
- Throttle position or accelerator pedal sensor fault setting engine-side codes
- Damaged or corroded wiring between the throttle sensor and the engine module
- Data bus line broken, shorted or with a bad connection between the modules
- Corroded or loose terminals in a module connector
- Weak battery or charging fault causing dropped messages between modules
- Poor module ground affecting signal reference
- Failed engine control module or a calibration mismatch after a replacement
How to fix it
- Scan all modules and record every stored code, engine side included
- Compare the throttle position value shown by the engine module with the value the transmission module receives
- Diagnose and repair any throttle or pedal sensor faults first, including their wiring and connectors
- Sweep the throttle slowly and watch for dropouts, spikes or a flat spot in the reported value
- Check battery voltage, charging output and module grounds
- Inspect the data bus wiring and connectors for corrosion, chafe and loose terminals
- Verify calibrations after any module change, then clear codes and confirm the transmission receives a smooth throttle signal