What does it mean?
P1590 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Throttle Actuation Potentiometer Signal Too Low (right side) .
Symptoms
- Check engine light on and a reduced power warning displayed
- Engine drops into limp mode with the throttle held at a low fixed opening
- Accelerator response is dead or extremely delayed
- Idle is unstable or the engine stalls when coming to a stop
- On engines with two throttle units, one side responds while the other does not, giving an uneven idle
- Vehicle will not reach normal road speed
Likely causes
- Signal wire shorted to ground along the harness route
- Loss of the 5 V reference feeding that potentiometer
- Worn or scored resistive track inside the throttle position sensor
- Corroded or water-filled connector at the throttle unit
- Terminal pushed back in the connector so contact is intermittent
- Carbon build-up that stops the throttle plate reaching its expected position
- Faulty reference or input circuit inside the control module
How to fix it
- Read both throttle potentiometer values in live data and compare them with each other and with the pedal position
- Inspect and reseat the throttle connector, checking for water, corrosion and backed-out terminals
- Measure the 5 V reference and sensor ground at the harness side with the ignition on
- Backprobe the signal wire and watch the voltage while slowly opening the throttle by hand where possible
- Test the signal wire for a short to ground with both ends disconnected
- Clean carbon from the throttle bore using the approved method and repeat the adaptation procedure
- Replace and code the throttle unit when the sensor track is proven faulty, then verify both channels agree