What does it mean?
P1121 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Throttle Position Sensor Intermittent High Input .
Symptoms
- Sudden surge or an unexpected jump in engine speed while driving at a steady throttle
- Brief loss of power followed by normal running, sometimes with a momentary limp mode
- Check engine light that comes on and clears again over several trips
- Erratic or harsh automatic transmission shifts
- Unstable idle and occasional stalling when lifting off
- Cruise control cutting out for no obvious reason
Likely causes
- Worn or dirty spot on the sensor's resistive track producing a voltage spike as the wiper passes over it
- Intermittent open in the sensor ground, letting the signal float toward reference voltage
- Signal wire touching the 5 V reference or a live circuit through a rubbed section of loom
- Moisture or corrosion in the throttle body connector that breaks contact with vibration
- Loose sensor mounting allowing the wiper to lift off the track
- Poor common ground affecting several sensors at once
- Module input fault, considered after the harness and sensor are proven
How to fix it
- Record the throttle position signal in live data with a fast graph while sweeping the throttle slowly through its full range and look for spikes
- Repeat the sweep while wiggling the connector and harness to reproduce the fault
- Check the sensor ground with a voltage-drop test, since a poor ground is a frequent cause of upward spikes
- Confirm the 5 V reference is steady and inspect the loom for chafing against the throttle body or a bracket
- Open the connector and check for moisture, corrosion and terminals that have lost tension
- Verify the sensor is tight on the throttle shaft and that the throttle plate moves freely without binding
- Replace the sensor or throttle body if the spikes follow the sensor, then complete the relearn procedure and re-test