The Throttle Position Sensor/Switch is located on the Throttle Body of the Intake Manifold and the Pedal Position Sensor/Switch is part of the Accelerator Pedal assembly.
These sensors tell the engine control module (PCM) how fast the driver wants to go and how quickly it needs to get up to speed.
When the PCM detects a problem with this sensor or the circuit for the sensor, it will set code P0120.
The PCM may also limit the speed of the vehicle to 20 miles per hour or less (“Limp home mode”) to protect the engine and the driver due to the control module’s inability to accurately detect the engine performance being requested.
What does code P0120 mean?
Diagnostic trouble code (DTC) P0120 stands for “Throttle/Pedal Position Sensor ‘A’ Circuit.” It is triggered once the powertrain control module (PCM) detects abnormal voltage readings from one of your car’s TP or APP sensors.
On vehicles of old, a cable connected the accelerator pedal to the throttle body 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.
Potential Symptoms of a P0120 Code
- Reduced engine power or acceleration
- Illuminated check engine light
- Stalling or difficulty starting the engine
- Poor engine performance or rough idling
Possible Causes:
- A faulty throttle/pedal position sensor or switch ‘A’
- Wiring or connections in the circuit may be damaged or faulty
- Loose or corroded electrical connections
- Failed engine control module (ECM)
How to Fix P0120?
One of the main causes of a triggered P0120 code is a faulty TP or APP sensor. It could be faulty wiring leading to the TP sensor.
To check whether your vehicle’s TP sensor is faulty, you’re going to need to check it with a multimeter. The TP sensor is typically mounted on the throttle body and is connected to the throttle body with screws.
The sensor also has a plug and connectors protruding from its side. The throttle body of some vehicles will be visible as soon as the hood is opened. However, this might not be readily accessible for some vehicles. You can check your owner’s manual to verify its location.
Once you’ve found the TP sensor, set your multimeter to its 10 DC voltage range and then place the black negative probe on the ground terminal of the TPS. Put the red positive prime on the reference voltage terminal of the TPS. If the multimeter doesn’t read 5 volts, then the TPS is faulty.
To fix the P0120 code, you’ll need to repair or replace the TP sensor. You might also need to repair any damaged wires that you might find.
To replace the TP sensor, simply pull out the sensor’s electrical connector by pushing down a tab on its side. Afterward, remove the TP sensor’s mounting screws using a screwdriver. Once the screws have been removed, you can remove the TP sensor.
To install the replacement TP sensor, simply insert the mounting screws on the sensor while they’re aligned with the screw holes. Then tighten the screws with a screwdriver. Reconnect the sensor’s electrical connector to complete the process.
How Much Does It Cost to Fix a P0174 Code?
The most common solution for the P0120 code is replacing the throttle position sensor. The average cost for a TPS replacement is between $100 and $200 (€85-€170), including parts and labor. The part itself typically costs between $50 and $100 (€40-€85).
If the issue is related to the throttle body or PCM, repair costs can be higher. Throttle body cleaning or replacement can range from $200 to $600 (€170-€510), while a PCM replacement can cost $500 to $1,500 (€425-€1,275).