Understanding P0120: Throttle Position Sensor/Switch A Circuit Malfunction

The P0120 code is a generic powertrain code related to the throttle or pedal position sensor/switch. But what does this mean, and how does it affect your vehicle? The answer to these questions lies in understanding the throttle position sensor’s role in your car’s functioning.

What is a Throttle Position Sensor?

The Throttle Position Sensor (TPS) is a critical part of your car’s engine management system. It’s a potentiometer, a type of resistor that adjusts the flow of electricity, located on the throttle body. The TPS informs the car’s computer about the position of the throttle.

How does the Throttle Position Sensor Work?

The TPS works in unison with the car’s Electronic Control Unit (ECU). When you press the accelerator, the throttle opens, and the TPS sends this information to the ECU. The ECU then instructs the fuel injectors to supply more fuel to match the increase in air entering the engine. This delicate balance of air and fuel ensures smooth engine operation and optimal fuel efficiency.

Recognizing P0120 Error Code

A P0120 error code indicates a potential issue with the Throttle Position Sensor’s circuit. This malfunction can significantly affect your car’s performance.

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Symptoms of a P0120 Error Code

The symptoms of a P0120 error code can vary, but they are usually noticeable. You may experience irregularities in engine performance, such as sudden surges in speed, engine misfires, or even stalling. Other symptoms can include a lack of power when accelerating, poor fuel economy, and the Check Engine Light illuminating on your dashboard.

Causes of the P0120 Error Code

Several factors can cause a P0120 error code. These range from a faulty throttle position sensor, poor electrical connections in the sensor’s circuit, or even a malfunctioning ECU.

Diagnostic Process for a P0120 Error Code

If you’re experiencing a P0120 error code, it’s essential to diagnose the issue correctly to avoid further damage to your vehicle. The process involves both initial and advanced diagnostic steps.

Initial Diagnostic Steps

The first step in diagnosing a P0120 error code involves using an On-Board Diagnostic (OBD) scanner. This tool retrieves the fault code and freeze frame data, which can provide useful information about the conditions when the error occurred.

A visual inspection of the throttle body, the TPS, and their connections is also crucial. Look for signs of damage, loose connections, or corrosion that could be causing the issue.

Advanced Diagnostic Procedures

If the initial diagnostics do not identify the problem, more advanced procedures may be necessary. These can include testing the sensor’s resistance with a digital multimeter, verifying the sensor’s voltage signal, or checking the ECU for faults.

How to Fix a P0120 Error Code

After diagnosing the cause of the P0120 error code, the next step is to fix the problem. The solution will depend on the diagnosis.

Basic Fixes

Basic fixes could involve cleaning the throttle body if it’s dirty, tightening loose connections, or replacing damaged wires. In some cases, resetting the ECU can resolve the issue.

Professional Repair Services

If the problem persists or is more complex, professional repair services may be necessary. This could involve replacing the throttle position sensor or even the ECU in extreme cases. It’s essential to rely on professionals for these tasks, as improper handling can cause further issues.

Preventing P0120 Error Code in the Future

While you can’t avoid every possible car issue, there are ways to minimize the risk of encountering a P0120 error code in the future.

Maintenance Tips

Regular maintenance of your vehicle is crucial. This includes routine cleaning of the throttle body and checking the condition of the TPS and its connections.

Regular Check-ups and Diagnostics

Regular check-ups and diagnostics can also help prevent issues. Using an OBD scanner periodically, even if you don’t notice any symptoms, can help detect potential problems early.


The P0120 error code is more than just a minor inconvenience—it can significantly affect your car’s performance. By understanding what causes this code, recognizing its symptoms, and knowing how to diagnose and fix the problem, you can ensure that your vehicle continues to function optimally.


What does the P0120 error code mean?

  1. The P0120 error code indicates a malfunction in the Throttle Position Sensor/Switch A Circuit.

What are the symptoms of a P0120 error code?

  1. Symptoms can include irregular engine performance, poor fuel economy, and the Check Engine Light illuminating on your dashboard.

How do I diagnose a P0120 error code?

  1. Diagnosis involves using an OBD scanner, conducting visual inspections, and potentially advanced diagnostic procedures like resistance and voltage checks.

How can I fix a P0120 error code?

  1. Fixes can range from cleaning the throttle body, tightening connections, replacing wires, or more complex solutions like replacing the TPS or ECU.

How can I prevent a P0120 error code in the future?

  1. Prevention includes regular vehicle maintenance, routine cleaning of the throttle body, and periodic check-ups and diagnostics.