What does it mean?
P1790 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: A/T Throttle Position Sensor Circuit Malfunction .
Symptoms
- MIL (check engine lamp) is on and shift points wander or change from one drive to the next
- No kickdown when the accelerator is pressed hard
- Harsh or unexpectedly late upshifts under light throttle
- Hesitation, surging or a flat spot at part throttle
- The transmission may fall into limp mode with a fixed gear
- Fuel consumption rises and the vehicle feels lazy
Likely causes
- Worn resistive track inside the throttle position sensor with a dead spot part way through its travel
- Sensor mounting or adjustment incorrect, so the closed-throttle value is out of specification
- Carbon build-up in the throttle body, meaning the reported angle no longer matches the real airflow
- Corroded or loose connector at the sensor, or spread terminals from repeated disconnection
- Open, shorted or high-resistance signal, reference or ground wire
- Adaptation values never relearned after cleaning, replacement or battery disconnection
- Control module input circuit fault
How to fix it
- Watch the throttle value in live data while opening the throttle slowly from closed to fully open and back, looking for glitches or dropouts
- Compare the closed-throttle value against specification and check it after the throttle body is clean
- Verify the 5 V reference and the ground at the sensor connector with the ignition on
- Check the signal wire back to the module for continuity, shorts and high resistance
- Inspect the connector for corrosion, moisture and weak terminal tension, and wiggle-test while watching data
- Fit and adjust or adapt a replacement sensor once wiring is proven, then confirm shift points on a road test