Subaru WRX P0120 Code: Meaning, Causes, How to Fix | Drivetrain Resource

Drivetrain Resource

The P0120 code on your Subaru WRX indicates an issue with the throttle position sensor (TPS).

This sensor plays a crucial role in your car’s performance, as it monitors the throttle valve opening percentage and provides input to the engine control module (ECM) to help regulate fuel and air intake.

When the P0120 code is triggered, it’s important to address the problem promptly to maintain your WRX’s performance and fuel efficiency.

Subaru WRX P0120

Some of the possible causes for the P0120 code in your Subaru WRX include an open or short in the throttle position sensor circuit, a faulty throttle position sensor, or issues with the ECM.

To diagnose and repair the problem, it’s essential to use an OBD II scan tool or a Subaru hand-held tester to confirm the throttle valve opening percentage and inspect related wiring harnesses and components for damage.

P0120 Meaning for the Subaru WRX

TPS “A” Circuit Malfunction

The P0120 code indicates an issue with the Throttle/Pedal Position Sensor “A” Circuit in your Subaru WRX.

This code appears when the sensor sends inadequate or erratic signals to the WRX’s onboard computer, affecting its performance.

Common P0120 Symptoms

P0120 symptoms subaru wrx

Experiencing a P0120 code in your Subaru WRX can be quite frustrating. Knowing the common symptoms associated with this code will help you identify the issue and take necessary steps to resolve it.

Here are some of the common symptoms you might encounter when the P0120 code appears:

  • Check engine light: The most obvious sign is your check engine light turning on. Whenever your vehicle’s engine control module (ECM) detects an issue, it triggers the check engine light.
  • Poor acceleration: You may notice that your Subaru WRX is not accelerating as it should. This can happen when the throttle position sensor (TPS) is not functioning properly, causing the ECM to receive incorrect input signals.
  • Unstable engine idle: A faulty TPS can lead to an unstable engine idle. Your vehicle may experience erratic idle speed or even stall at idle.
  • Reduced fuel efficiency: Since the TPS is responsible for regulating air-fuel mixture, a malfunctioning sensor can result in decreased fuel efficiency.

In many cases, cleaning your WRX’s throttle body can help resolve the issue. However, if the code reappears after cleaning, you may need to replace the Throttle Body Assembly.

P0120 Causes: Subaru WRX

When you encounter a P0120 code in your Subaru WRX, it might be due to several reasons. Understanding these potential causes will help you streamline your troubleshooting process and address the issue effectively.

Let’s take a look at some of the possible causes for the P0120 code in the Subaru WRX.

  • Open or short in throttle position sensor circuit: An open or shorted throttle position circuit can cause the P0120 code to appear. Inspect the wiring and connectors for any signs of damage or corrosion.
  • Faulty Throttle position sensor: A faulty throttle position sensor can also trigger the P0120 code. This sensor is responsible for measuring the throttle valve opening percentage, and if it fails, it can lead to an incorrect reading and the subsequent appearance of the P0120 code.
  • ECM issues: The Engine Control Module (ECM) is a crucial component of the engine management system. If there’s a problem with the ECM, such as a software or hardware malfunction, it might cause the P0120 code to show up.


To address the P0120 code, start by visually inspecting the related wiring harness and connectors for any signs of damage, corrosion, or bent pins.

If you find a problematic point, attend to it immediately. Also, consider using an OBD II scan tool or a Subaru hand-held tester to confirm the throttle valve opening percentage.

This data will help you determine whether you need to replace your WRX’s throttle position sensor or if the issue lies elsewhere.

Remember to take a methodical approach and make sure to rule out any other potential causes before pinpointing the source of the problem.

Diagnostic Procedure

P0120 Diagnosis

To diagnose the P0120 code in your Subaru WRX, follow these steps:

  1. Identify the symptoms: Experiencing an erratic high idle, check engine light, and potential issues with acceleration can indicate the presence of a P0120 code.
  2. Use a scan tool: Connect an OBD-II scan tool or TOYOTA hand-held tester to the vehicle. This will help you read and confirm the Diagnostic Trouble Code (DTC) P0120.
  3. Check the throttle position sensor (TPS): Inspect the TPS, which is mounted on the throttle with motor body assembly. Look for signs of damage or wear, as a faulty TPS can cause this code to appear.
  4. Inspect the TPS circuit: Check for an open or short in your WRX’s throttle position sensor circuit. This can also generate the P0120 code.
  5. Evaluate the ECM: There could be a rare chance that the Engine Control Module (ECM) is causing the problem, so consider the ECM in your diagnosis process.

By following these steps, you can identify and rectify the possible causes of the P0120 code in your Subaru WRX. Remember, it’s crucial to address this issue to maintain your vehicle’s optimal performance and ensure safe driving conditions.


P0120 in the Subaru WRX can be diagnosed at home with a little knowledge and a lot of patience. Good luck!

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