What does it mean?
P1591 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Throttle Actuation Potentiometer Signal Too High (Right Side) .
Symptoms
- Check engine light on with a reduced power or throttle warning
- Engine enters limp mode and will not respond normally to the pedal
- Idle speed unusually high, or the engine races when started
- Poor and unpredictable throttle response, with the vehicle surging
- On twin throttle engines the two sides disagree, giving a rough idle
- Engine may refuse to rev beyond a low limit
Likely causes
- Signal wire shorted to battery voltage or to the 5 V reference inside a damaged connector
- Open sensor ground, which lets the signal rise to the top of its range
- Internally failed potentiometer stuck at maximum output
- Corrosion bridging the terminals in the throttle connector
- Chafed harness contacting an adjacent live circuit
- Throttle plate mechanically jammed open by carbon or a foreign object, producing a genuine high reading
- Faulty input circuit inside the control module
How to fix it
- Compare both throttle potentiometer signals in live data at closed throttle and note which one sits high
- Unplug the throttle unit and check whether the signal falls, which separates a wiring short from a sensor fault
- Measure the sensor ground for continuity and voltage drop back to the module
- Test the signal wire for a short to battery voltage and to the reference line with both ends disconnected
- Inspect the connector for corrosion bridging the pins, and clean or repair the terminals
- Check the throttle plate for mechanical jamming, carbon build-up or a foreign object in the bore
- Replace and code the throttle unit if the sensor is proven faulty, then run the adaptation and confirm both signals track