What does it mean?
P1120 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Throttle Position (TP) Sensor A Out Of Range Low (Ratch Too Low) .
Symptoms
- Check engine light on and the vehicle dropping into limp mode
- Engine will not rev beyond a limited speed and acceleration is very weak
- Unstable idle, surging or stalling when coming to a stop
- Harsh or delayed automatic transmission shifts, because shift control uses the throttle signal
- Throttle pedal feels dead over part of its travel
- Cruise control disabled
Likely causes
- Open or missing 5 V reference feed to the throttle position sensor
- Signal wire shorted to ground in a chafed section of the throttle body harness
- Worn resistive track inside the sensor, most often at the closed-throttle end where it spends most of its life
- Corroded or water-damaged throttle body connector
- Poor sensor ground or a high-resistance shared ground point
- Loose or incorrectly fitted sensor on the throttle shaft after previous work
- Failed module input, checked only when the wiring and sensor test good
How to fix it
- Graph the throttle position value while slowly opening the throttle from closed to fully open and look for a value stuck at or near zero
- Unplug the sensor and check for 5 V on the reference pin with the ignition on; no reference sends the diagnosis back toward the module
- Check the signal wire for a short to ground with the sensor disconnected
- Voltage-drop test the sensor ground and clean the shared ground point if the drop is high
- Inspect the connector for corrosion, moisture and spread terminals
- Confirm the sensor is correctly seated and secured on the throttle shaft
- Replace the throttle position sensor or the throttle body as required, then carry out the throttle relearn procedure and verify a smooth sweep