What does it mean?
P1799 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Throttle Position (TP) sensor Malfunction .
Symptoms
- MIL (check engine lamp) is on and the engine hesitates or surges at a steady part throttle
- Idle hunts up and down or settles too high
- No kickdown and shift points that are clearly wrong
- Harsh or delayed shifts under acceleration
- Reduced power mode on vehicles with electronic throttle
- The fault often appears only in one part of the pedal travel
Likely causes
- Worn resistive track with a dead spot, typically in the range the vehicle spends most time in
- Closed-throttle value out of specification because the sensor is misaligned or incorrectly fitted
- Carbon build-up around the throttle plate holding it away from its rest position
- Corroded or loose sensor connector, or terminals spread from repeated removal
- Damage to the sensor from moisture, pressure washing or engine bay steam cleaning
- Missing 5 V reference or a poor sensor ground shifting the whole signal range
- Adaptation values never reset after the throttle body was cleaned or replaced
How to fix it
- Open the throttle slowly from closed to fully open while watching the signal voltage or percentage for any drop or jump
- Compare the closed-throttle value against specification, before and after cleaning the throttle body
- Verify the 5 V reference and the sensor ground at the connector with the ignition on
- Inspect the connector for corrosion, moisture and terminal tension, and wiggle-test while watching the reading
- Where the sensor is adjustable, set it to specification and recheck the closed value
- Fit a new sensor once the wiring is proven, then carry out the adaptation or relearn procedure and road test