Signs of a Bad Accelerator Pedal Position Sensor, Diagnosis, and Fixes

Knowing the Signs of a bad accelerator pedal position sensor, how to diagnose and fix it will save you from rough idling, inconsistent acceleration, amongst others. APP sensor serves as a determiner and connector between the driver and the ECU – basically the brain of a vehicle.

It signals the ECU to allow more air-fuel mixture ratio to the engine through the throttle body in accordance with the gas pedal position. It is normal for a car to accelerate as the driver depresses the gas pedal until it doesn’t. In any case, several factors can prevent acceleration or cause rough idling, but it can be challenging to track down the cause.

The most common cause of this problem could be a defective APP sensor or issues with the throttle position sensor. This article will discuss at length the signs of a failing APP sensor and how to diagnose and fix it.  Sit back and have a 5-minute read.

Signs of a bad accelerator pedal position sensor

Like most electrical and mechanical vehicle components, a failing or faulty APP sensor will showcase a series of signs that will alert the driver that a problem exists in the system. “Accelerator pedal position sensor problems” are as follows;

signs of bad accelerator pedal position sensor

Rough Idling:

If your vehicle doesn’t run consistently on idle, there are chances that you have a faulty accelerator pedal position (APP) sensor. A perfect working APP sensor is necessary for good fuel delivery and consistent or smooth idling.

Your vehicle doesn’t accelerate over a specific limit:

Suppose your baby ride accelerates up to a point and won’t go above that speed; it indicates your APP sensor isn’t able to send accurate throttle positioning signals. The result is poor engine performance.

The engine does not run effectively:

If the accelerator pedal position sensor is working inappropriately, it will have problems with fuel efficiency. Aside from sending the driver’s input to the throttle body, it stabilizes the throttle control.

It is designed to take command from the driver and maintains a steady fuel pressure as it sends the driver’s input to the ECU, then to the throttle body. If the sensor fails to send appropriate readings due to a loose wire, corroded connectors, or broken wires, it will negatively affect your fuel economy.

Inconsistent acceleration:

When you depress the gas pedal, your engine should respond immediately. But if the accelerator pedal position sensor fails, the car’s ability to instantly accelerate or decelerate as the driver depresses the gas pedal will drastically reduce. This can cause road hazards as the driver does not have complete control of the vehicle.

You need to stop driving once you notice inconsistent acceleration. If uneven acceleration occurs, ensure you pull your car off the road in a safe place and contact your dealership or mechanic to diagnose and fix the problem.

Poor automatic transmission shifting or jerks when depressing the throttle pedal:  

A malfunctioning APP sensor will send a false signal to the transmission computer. Depressing a gas pedal with a bad sensor will give delayed signals or burst varying signals, leading to poor gear shifting.

Check engine light:

Since the accelerator pedal position sensor is an electrical component monitored by the car computer, it will trigger a fault code on the computer when something goes wrong. You’ll be able to notice there’s a registered fault when the check engine light comes on.

For your car ECU to work as it should, all the electrical sensors in your vehicle need to be in good working condition. A malfunctioning APP sensor will register a P2135 diagnostic trouble code. Several reasons can trigger this code, and you will need a certified mechanic to diagnose the real cause of the code in your situation.

How the accelerator pedal position sensor works

Modern cars use electronic systems to send signals from the gas pedal to the ECU and throttle body instead of using a cable between the gas pedal and throttle body.

A driver determines the rate of a car’s speed by continually depressing the accelerator pedal, which signals the throttle body to allow the more air-fuel mixture to go in.

The “throttle position sensor” and the APP sensor monitor the throttle body valve positioning and signals to the ECU. Then, the ECU works with that signal to determine the needed air/fuel mixture ratio and open the throttle valve following the accelerator pedal position, RPM, current speed, MAF readings, and air temperature.

The outcome is an excellent and smooth driving experience. Therefore, it is essential to maintain “the accelerator pedal position sensor” working principle. Some vehicles are equipped with both TPS on the throttle body and APP sensors on the gas pedal, while others only have throttle position sensors on the throttle body.

It is crucial to ensure the TPS works as it should because it can reduce the gas economy and overall engine performance. Where is the APP located?

Knowing the accelerator pedal position sensor location is essential for diagnosing and replacement purposes. The APP sensor is attached to the throttle pedal. In most cars, you can replace only the APP sensor, while other cars require replacing the gas pedal as a whole.

How to test accelerator pedal position sensor

Let’s look at how to carry out accelerator pedal position sensor testing. If you’re experiencing two or more of the signs above, you’re likely to have a failing or lousy accelerator pedal position sensor. Let’s get started with the testing process.

symptoms of bad accelerator pedal position sensor

Locate the APP sensor:

The first step in diagnosing the APP sensor is to locate it. The APP sensor is located beneath the driver’s side dashboard. It is attached to the gas pedal.

As you already know, vehicles are manufactured by several automakers with different designs.  Some APP sensors can be replaced as a single unit, while others are not detachable from the gas pedal.

Inspect the wiring harness:

Wiggle the connectors and see if any of the wires are loose. If everything seems okay, unplug the wiring harness and visually inspect the electrical connectors for Rust and Corrosion. Any Corrosion on the connectors can lead to several other issues, and of course, that can cause electrical resistance.

The APP sensor uses low voltage to send a signal to the computer – basically, it’s not going to be 12 volts. It’s a 5 volts system.

Test the wires with a multimeter:

You want to test the wires if they are good. Contact the meter probes against each other and listen for a beep to ensure the meter is working. Set the meter on Ohms scale and turn on the beep. Slide off the wiring harness to gain full access to the connectors.

With the cover off, you have to place the red probe on the connectors individually. The connectors make contact with the pedal. Place the black probe on the vehicle ground and test the purple wire with the red probe. It should be less than 5 ohms. Locate the brown wire and test it as well. You need to carry out this test with the ignition off.

If you find a vast difference in the results, for instance, you have one that is 4.1, and another one is 0.4, you need to check the wire.

Switch the meter to DC volts. You have to check another two wires. Now, turn the ignition to ON position – do not start the vehicle. Locate the black and white wire and test them. While the meter black probe is still connected to the ground, touch the red probe on the white and black connectors, respectively. The readings should be around 4.9 or 4.8.

If both readings are low, you have to ensure your battery is recharged. Your battery should be at least 12 volts before running this test. If it is less than that, you have to charge it.  If you don’t see anything wrong with the wire, you will have to replace the APP sensor itself.

So how do I replace the APP sensor? You will find the answers in the following few paragraphs.

How to fix bad accelerator pedal position sensor

Accelerator pedal position sensor replacement is a simple task for an average mechanic. Fixing a lousy APP sensor entails replacing the defective sensor with a new one. Before installing the new sensor, you need some essential hand tools.

Needed Tools:

Needed parts:

  • Replacement accelerator pedal position sensor.

Let’s get started on the replacement process.

Disconnect the negative battery terminal:

Like I always advise, disconnect the negative battery terminal before working on any electrical components. This will prevent electrical jolts and unwanted shocks to you and damages to other electrical system components.

Remove old APP sensor:

Locate the APP sensor on the gas pedal and unplug the wiring harness that sends signals to the ECU. Ensure you unplug it carefully by pressing down the knob and pulling off the connectors to avoid cutting the wires.

Remove installation screws:

Once the wiring harness is out of the way, unscrew the installation screws that hold the sensor. Keep the screws in a safe container if you intend to reuse them to reinstall the new sensor.

Remove the old APP sensor:

Gently pull out the old sensor and dispose of it properly. Ensure you don’t obstruct your local regulations.

Compare both sensors:

It is advisable to compare old and new components before installation. This is usually important when you’re replacing a component with aftermarket parts. Therefore, place both sensors together and ensure the new sensor will fit in.

Install the new APP sensor:

Following the reverse process, install the new sensor to where you removed the old one.

Re-plug the electrical connectors:

Gently re-plug the electrical connector into the new APP sensor. Pay close attention to connectors and chips and ensure they are well-aligned for proper installation.

Reconnect the negative battery terminal:

Reconnect the negative cable and tighten it with a sizable wrench set.

Test your work: Once you’re done with the installation process, have a moment of doubt and recheck your work. Run a test and see if the job paid off. Congrats, you’ve successfully replaced your bad APP sensor.


How much does it cost to replace the accelerator pedal position sensor?

The average APP sensor replacement is between $90 and $300, depending on your vehicle’s make and model. The APP sensor itself should be $40-$200, and the service charge around $50-$100.

The cost of the sensor differs a lot because some vehicles have an APP sensor as a single unit while others require changing the gas pedal, which makes it more expensive.

How do I reset my accelerator pedal?

Timing is highly critical in resetting the APP sensor. If the process is not done within a specified time, it may not reset.

Resetting procedures

  • Make sure the gas pedal is not depressed. Ensure it is fully released.
  • Switch the ignition to the ON position and wait for 2-5 seconds.
  • Switch the ignition to the OFF position and wait for 10 seconds
  • Switch the ignition to the ON position and wait for 2-5 seconds.
  • Switch the ignition to the OFF position and wait for 10 seconds

How do I reset my accelerator pedal sensor?

It is essential to calibrate the ECU and the gas pedal when you replace it with a new one. A new calibration is downloaded on the ECU when a gas pedal is installed or when the electrical connector disconnects while the ignition is in the ‘ON’ position. So, how do I calibrate my accelerator pedal position sensor?

To successfully calibrate the ECU and the gas pedal sensor, you have to turn the ignition to the ‘ON’ position and slowly depress and release the gas pedal. Repeat this process a couple of times.

Where is the accelerator pedal position sensor?

The accelerator pedal position sensor signals the throttle body how far the driver wants it to open when he depresses the pedal. So, where is it in your vehicle? The APP sensor is attached to your gas pedal beneath the driver’s side dashboard.


Now you know one of the major causes of inconsistent acceleration, rough idling or car works fine but won’t exceed a certain low speed, and problems with the automatic transmission shifting.

Always watch out for a lousy accelerator pedal position sensor and fix it right away. In your situation, whether you replace the electrical connectors, replace the accelerator pedal, or repair those wires, after that, you should be good to go.

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Osuagwu Solomon

Osuagwu Solomon is a certified mechanic with over a decade of experience in the mechanic garage, and he has over five years of experience in the writing industry. He started writing automotive articles to share his garage experience with car enthusiasts and armature mechanics. If he is not in the garage fixing challenging mechanical problems, he is writing automotive repair guides, buyer’s guides, and car and tools comparisons.

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