P1121
Throttle Position Sensor Signal Invalid
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The P1121 code on Hyundai and Kia vehicles means the Engine Control Module (ECM) has detected an invalid or inconsistent signal from the throttle position sensor (TPS). The TPS tells the computer how far open the throttle plate is, which directly affects fuel delivery, ignition timing, and transmission shift points. When the signal is erratic or out of expected range, the engine management system cannot properly control these functions.
This code is particularly common on Kia Sorento and Sedona models, where the internal elements of the TPS can wear prematurely, especially in hot climates. The increased contact resistance from this wear causes intermittent high voltage spikes. In many cases, a thorough cleaning of the throttle body resolves the issue, as carbon deposits can interfere with proper throttle plate movement and sensor readings.
While the vehicle may still be drivable, you'll likely experience reduced performance and possibly limp mode. Start with the simplest fix — cleaning the throttle body — which is an easy DIY job requiring only throttle body cleaner and basic tools. If the code returns after cleaning, the TPS itself likely needs replacement, which is an affordable and straightforward repair on most Hyundai and Kia models.
Severity
Symptoms
- •Reduced acceleration or lack of response when pressing gas pedal
- •Engine stalling or rough idling
- •Vehicle may go into limp mode
- •Hesitation or jerky acceleration
- •Noticeably reduced fuel economy
Likely Causes
In Kia Sorento and Sedona models, excessive wear of the inner elements of the TPS causes increased contact resistance, especially in hot ambient or desert conditions, resulting in an invalid signal.
Carbon buildup on the throttle plate prevents smooth operation and causes the TPS to report inconsistent voltage readings to the ECM.
Damaged wiring, loose connectors, or corroded pins between the TPS and ECM cause intermittent signal dropout and erratic voltage values.
On some models, P1121 specifically refers to an abnormal throttle position signal from the ECM to the transmission control module, which can be caused by CAN bus faults or module issues.
Estimated Cost
Professional Repair
Includes parts + labor
Common Fixes
- Clean the throttle body thoroughly with throttle body cleaner
- Replace the throttle position sensor
- Inspect and repair corroded or damaged wiring connectors
- Check for and address any related TPS or ETS codes