Error Code P2120 is defined as Throttle/Pedal Position Sensor/Switch D Circuit, a problem usually caused by issues in the wiring, APP/TP sensor or switch, short to positive, short to ground, or problems in the HO2S or PCM.

This error code is a generic trouble code, meaning it applies to all vehicles equipped with OBD-II system, especially those made since 1996 up to present. Specifications on the definition, troubleshooting, and repairs, of course, vary from one make and model to another.


This error code happens when the PCM (powertrain control module, also known as ECM or engine control module) has detected a major failure problem in the Throttle Pedal Position (TP) sensor circuit caused by above or low voltage return as specified from the sensor.

Common Symptoms

As with other error codes, this code activates the Check Engine light on the dashboard and registers the code to the vehicle’s memory. Other symptoms include:

  • Poor acceleration
  • Slow throttle response
  • Low RPM

Symptoms of the vehicle usually depend on the manufacturer’s Failure Mode; some vehicles may experience idle only, limited power and limited throttle opening.

Possible Causes

This means the PCM is getting a voltage return that is lower than 0.24V or more than 4.49V coming from the Throttle Pedal Position sensor, which indicates the latter being out of range of its specifications and causes the PCM to limit throttle opening by going into Failure Management mode.

How to Check

To diagnose this error code, mechanics use the scan tool to scan and document the code in the PCM and record the freeze frame data for failure.

Then, they conduct a diagnosis for the code as specified by the vehicle manufacturer’s pinpoint test.

Lastly, they check the scan data of the TPS (throttle position sensor) to see whether it is getting the right reference voltage or not, and if it is sensing the throttle angle properly.

How to Fix

Repairs for this code are pretty simple and straightforward. But of course, still require thorough diagnosis. Repairs include:

  • Replacement of the throttle position sensor
  • Repairing of the open or shorted connector or sensor wiring

Error Code P2120 means the PCM has detected a major throttle position problem (failure) and will be under Failure Management mode. This means the vehicle will have limited RPM since the throttle control actuator system depends on the pedal position sensor to control the throttle.

After fixing this code, the PCM must be cleared of the code for a thorough repair.