P0120 – Throttle Position Sensor Circuit Malfunction

The P0120 engine code indicates a problem with the throttle position sensor (TPS) or its circuit. This code is triggered when the powertrain control module (PCM) detects an abnormal voltage from the TPS.

Urgency and Severity

When the P0120 code is detected, it's generally safe to continue driving in the short term. However, you may experience reduced engine performance, rough idling, or stalling. It's best to diagnose and fix the issue as soon as possible to prevent further damage and avoid potential safety issues. If the problem persists or worsens, it's advisable to visit a mechanic or dealer for professional assistance.

Code Specifics

The P0120 code is a generic powertrain code, which means it applies to all makes and models of vehicles manufactured after 1996. However, the specific repair procedures and part numbers may vary depending on the vehicle make and model.

Parts Involved

The main component associated with the P0120 code is the throttle position sensor (TPS). The TPS is typically located on the throttle body and measures the throttle valve angle, providing this information to the PCM to control fuel injection, ignition timing, and other engine parameters.

Common Causes

Some common causes of the P0120 code include:

• Faulty throttle position sensor
• Damaged or corroded TPS wiring or connectors
• Throttle body issues (e.g., carbon buildup, mechanical problems)
• PCM software issues or failure

Diagnosing the P0120 Code

To diagnose the P0120 code, follow these steps:

1. Visually inspect the TPS wiring and connectors for damage, corrosion, or loose connections. Repair or replace as needed.

2. Test the TPS using a multimeter:

   • Disconnect the TPS and measure the resistance between the reference voltage and ground pins. It should be within the manufacturer's specifications (typically 3-7 kΩ).
   • Measure the output voltage while slowly opening the throttle. It should increase smoothly from about 0.5V (closed) to 4.5V (fully open).

3. If the TPS tests fail, replace the sensor. If the tests pass, check for issues with the throttle body or PCM.

Solutions and Repair Costs

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) or more.

Prevention and Related Issues

To prevent TPS-related issues, regularly inspect the throttle body and clean it if necessary to remove carbon buildup. Also, address any other engine issues promptly, as they can lead to increased wear on the TPS.

Other fault codes that may appear alongside P0120 include:

• P0121: Throttle position sensor range/performance problem
• P0122: Throttle position sensor circuit low input
• P0123: Throttle position sensor circuit high input

Repair Guide

For a step-by-step guide on replacing the throttle position sensor, consult your vehicle's repair manual or refer to online resources specific to your make and model. Always disconnect the battery before working on electrical components, and ensure the new TPS is properly calibrated after installation.

When working on the throttle body, take care not to damage the throttle plate or bore. If cleaning the throttle body, use a specialized throttle body cleaner and avoid spraying cleaner directly onto the TPS.

Frequently Asked Questions About P0120

What does the P0120 code mean?

The P0120 code indicates a problem with the Throttle Position Sensor (TPS) or its circuit. The code is triggered when the powertrain control module (PCM) detects an abnormal voltage from the TPS that falls outside the expected range.

Is it safe to drive with a P0120 code?

While it’s generally safe to drive with a P0120 code in the short term, you may experience reduced engine performance, rough idling, or stalling. It’s best to diagnose and fix the issue as soon as possible to prevent further damage and avoid potential safety issues.

What are the common symptoms of a P0120 code?

Common symptoms include:

• Poor acceleration
• Rough idling or stalling
• Difficulty starting the engine
• Increased fuel consumption
• Jerking or bucking during acceleration
• Difficulty shifting gears (in automatic transmissions)

What causes a P0120 code?

Possible causes of a P0120 code include:

• Faulty throttle position sensor
• Damaged or corroded TPS wiring or connectors
• Throttle body issues (e.g., carbon buildup, mechanical problems)
• PCM software issues or failure

How do I diagnose a P0120 code?

To diagnose a P0120 code:

1. Visually inspect the TPS wiring and connectors for damage, corrosion, or loose connections. Repair or replace as needed.
2. Test the TPS using a multimeter to check resistance and output voltage.
3. If the TPS tests fail, replace the sensor. If the tests pass, check for issues with the throttle body or PCM.

What is the average cost to fix a P0120 code?

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). Costs may be higher if the issue is related to the throttle body or PCM.

Can a dirty throttle body cause a P0120 code?

Yes, a dirty or carbon-filled throttle body can cause issues with the TPS, leading to a P0120 code. Cleaning the throttle body may resolve the problem in some cases.

How often should I replace my throttle position sensor?

There is no specific interval for replacing the TPS. It should be replaced when it fails or when diagnosed as the cause of a P0120 code.

Can a faulty TPS cause transmission problems?

Yes, a faulty TPS can cause issues with automatic transmission shifting, as the TPS signal is used by the transmission control module to determine the appropriate gear.

What other codes may appear alongside P0120?

Other related codes that may appear with P0120 include:

• P0121: Throttle position sensor range/performance problem
• P0122: Throttle position sensor circuit low input
• P0123: Throttle position sensor circuit high input

Can a P0120 code cause the check engine light to come on?

Yes, when the PCM detects a problem with the TPS or its circuit, it will trigger the check engine light along with storing the P0120 code.

Is it necessary to replace the throttle body when replacing the TPS?

In most cases, replacing the TPS alone will resolve the P0120 code. However, if the throttle body is heavily contaminated or damaged, it may also need to be replaced or cleaned.

Can a P0120 code cause limp mode?

Yes, some vehicles may enter a “limp home” mode when a P0120 code is detected, limiting engine performance to prevent further damage and allow the driver to safely reach a service location.

How do I clear a P0120 code?

After diagnosing and repairing the issue causing the P0120 code, you can clear the code using an OBD-II scanner or by disconnecting the battery for a few minutes. However, if the underlying problem is not fixed, the code will likely reappear.

Can a malfunctioning TPS cause poor fuel economy?

Yes, a faulty TPS can lead to an incorrect air-fuel mixture, resulting in reduced fuel efficiency and increased fuel consumption.

Is it possible to test a TPS without removing it from the vehicle?

In some cases, you can test the TPS using a multimeter without removing it from the vehicle. However, for a more thorough inspection and testing, it’s often necessary to remove the sensor.

Can a P0120 code be caused by issues with the accelerator pedal?

While less common, problems with the accelerator pedal or its position sensor can sometimes lead to a P0120 code, as the pedal position sensor and TPS work together to determine the desired throttle position.

How does the TPS work with other engine components?

The TPS works in conjunction with other sensors, such as the mass airflow sensor (MAF) and manifold absolute pressure (MAP) sensor, to provide data to the PCM for controlling fuel injection, ignition timing, and other engine functions.

Can a P0120 code be caused by a vacuum leak?

While a vacuum leak is not a direct cause of a P0120 code, it can lead to erratic engine behavior and may exacerbate issues related to a faulty TPS.

What should I do if the P0120 code returns after replacing the TPS?

If the P0120 code persists after replacing the TPS, there may be an underlying issue with the throttle body, wiring, connectors, or PCM. Further diagnostic testing will be necessary to identify and resolve the problem.