Diagnostic Trouble Code P0120

P0120 “Throttle/Pedal Position Sensor/Switch A Circuit”


What is code P0120?

Code P0120 stands for “Throttle/Pedal Position Sensor/Switch A Circuit”. This diagnostic trouble code can show up for a number of reasons that have to do with the throttle position sensor and accelerator pedal position sensor. Therefore, it is important to have a qualified technician diagnose the specific problem that caused the code to be stored in your vehicle’s computer.

Get this checked out soon by a CarAdvise shop, where the work will be guaranteed, and one of our expert techs will review any repair orders.

What does code P0120 mean?

A technician understands that code P0120 on a diagnostic scan of your vehicle means that there is something going on with one of the sensors that enable the throttle on most modern vehicles to work.

On vehicles of old, a cable connected the accelerator pedal to the throttle body (or carburetor on even older models) on an engine. There was a physical connection between the pedal under the driver’s foot and the throttle. Today’s automobiles, however, feature a system of sensors that control throttle operation. One sensor, the accelerator pedal position (APP) sensor (mounted on the accelerator pedal assembly), detects how far you press the gas pedal. The throttle position sensor (TPS) is mounted on the throttle body on your engine and detects how far the throttle plate is open. It is not uncommon for an engine to rely on two throttle position sensors.

Together, the APP sensor and TPS work to deliver data from the accelerator pedal and the throttle body to the ECM (Engine Control Module). When you press the accelerator pedal, the information is sent to the ECM which, in turn, controls the throttle body and other functions. This arrangement is termed “drive-by-wire” technology. Whenever your engine is running, data from these sensors is sent continuously to the ECM. The data should mirror what the driver is commanding through the accelerator pedal. The ECM uses the data to determine how much power the engine should be making. This correlates to how far the throttle plate opens (in combination with the throttle position sensor), how much fuel is injected into the cylinders, when the spark plugs are fired, and more.

Code P0120 is the generic code for when the data sent to the ECM is outside of its normal range. 


What causes code P0120?

A number of causes can trigger a code P0120. That is why an accurate diagnosis is essential. Causes of this code include:

Most likely

Other possibilities

  • Corrosion on the sensor connector or ECM connector
  • Torn or jammed floor mats
  • Stuck accelerator or throttle return spring
  • Bad ECM


What symptoms are associated with this code?

Common signs associated with a code P0120 include the following:

  • The check engine light is on or flashing
  • Your engine enters “limp” mode and will not accelerate
  • Engine idles higher than normal
  • Transmission shifts incorrectly
  • Vehicle is hard to start
  • Engine runs roughly or hesitates on acceleration


How does a technician diagnose code P0120?

If a diagnostic scan of your vehicle indicates a code P0120, a technician will perform tests to pinpoint the problem. These tests include checking for any related trouble codes. The technician will also use the scan tool to view live data from the APP sensor to determine whether or not it is consistent while manually pressing on the pedal with the engine off. The wiring from the ECM to the sensor will be inspected for cracks, corrosion, contamination, or bent pins on the connectors. The technician might also perform tests on the APP sensor or TPS with a multimeter and verify that adequate voltage is reaching the sensor when it is in operation.


How serious is this code?

In some cases, you might not notice any symptoms when a code P0120 is present. Otherwise, symptoms might be intermittent. If your vehicle is placed by the ECM into failsafe “limp” mode, you will be unable to accelerate. The engine might run roughly. This problem should be addressed as soon as possible.

Get this checked out soon by a CarAdvise shop, where the work will be guaranteed, and one of our expert techs will review any repair orders.


Related Diagnostic Trouble Codes

P0122 Throttle/Pedal Position Sensor/Switch A Circuit Low

P0123 Throttle/Pedal Position Sensor/Switch A Circuit High

P0124 Throttle/Pedal Position Sensor/Switch A Circuit Intermittent


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