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.
What’s the Accelerator Pedal Position Sensor?
The accelerator pedal position sensor is one of the parts that comprise the gas pedal. It’s also called the accelerator pedal sensor or APP sensor.
Most pedal position sensors are non-conductive devices. Their internal components don’t need to come into physical contact during operation.
Typically, an accelerator pedal position sensor comprises a stator and a rotor. The stator is the more complex component, possessing several coils and an electronic evaluation unit that checks the sensor’s status.
Only automatic vehicles with an ETC possess an accelerator pedal position sensor. Other automatic vehicles rely on different sensors to measure the throttle opening and the volume of air passing through it.
Meanwhile, manual vehicles use a mechanically-based approach to control the throttle.
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.
Accelerator Pedal Position Sensor Location
The accelerator pedal position sensor is located inside the accelerator pedal. In some cases, it is possible to replace just the sensor, but on other car models, you have to replace the whole accelerator pedal.
Removing the accelerator pedal can sometimes be challenging, but it is pretty straightforward on most car models.
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;
#1. Unresponsive or Delayed Acceleration.
This is the most common symptom you’ll notice with a failing APP sensor. When you push down on the gas pedal, there’s a noticeable delay before the engine responds, or it may not respond at all.
You might find yourself pressing harder on the pedal just to get a normal acceleration response.
Because the sensor isn’t accurately reading your pedal position or sending only intermittent signals to the ECU, the computer doesn’t know how much throttle you’re requesting, so it defaults to a conservative response.
This delay can be particularly dangerous when merging onto highways or trying to pass other vehicles where quick acceleration is needed for safety.
#2. Check Engine Light.
A malfunctioning accelerator pedal position sensor will usually (but not always) trigger the check engine light on your dashboard. This is one of the earliest warning signs, as the ECU continuously monitors the sensor for proper operation and will detect inconsistencies in the signal.
Common error codes related to APPS failure include P2135 (throttle/pedal position sensor voltage correlation), P2138 (throttle/pedal position sensor correlation), and P0223 (throttle/pedal position sensor circuit high input).
I you drive a Volkswagen, Audi, or other vehicle part of the VAG family, an EPC light may also appear.
Getting these codes scanned at an auto parts store or with an OBD-II scanner can help confirm the diagnosis. Don’t ignore this warning light, as it indicates the ECU has detected a problem that could affect vehicle safety and performance.
#3. Limp Mode Activation.
When the ECU detects serious problems with the accelerator pedal position sensor, it may activate limp mode as a safety measure.
In limp mode, your vehicle’s performance becomes severely limited (typically limiting engine RPM to around 2,000-3,000 and reducing available power).
This protective feature prevents potential damage to the engine and transmission while allowing you to drive to a repair shop at reduced speeds. Your car will exhibit sluggish acceleration and may not be able to exceed 35-45 mph (depending on the manufacturer).
While frustrating, limp mode serves an important safety function by preventing unpredictable acceleration behavior that could lead to accidents. The mode will remain active until the underlying sensor problem is repaired.
#4. Rough or Inconsistent Idle.
When your APP sensor starts failing, you may notice your engine idling roughly or inconsistently. The RPMs might fluctuate between 500 and 1,200 while sitting at a stoplight, or the engine may feel like it’s struggling to maintain a steady idle speed.
This occurs because the ECU relies on input from the accelerator pedal position sensor to help control idle speed, even when you’re not touching the pedal.
A faulty sensor can send conflicting signals, making the computer think you’re lightly pressing the accelerator when you’re not.
The engine control module then tries to compensate by adjusting fuel delivery and air intake, resulting in an unstable idle that can be both annoying and concerning.
#5. Car Won’t Start or Starts Then Stalls.
A completely failed APP sensor can prevent your vehicle from starting altogether, or cause it to start and immediately stall.
This happens because the ECU can’t determine the accelerator pedal’s position, so it doesn’t know whether you’re intentionally pressing the gas or not.
As a safety feature, many vehicles won’t start if the computer can’t get a proper reading from the accelerator pedal position sensor. This prevents unintended acceleration during startup.
If your car does start, it may run for a few seconds before the ECU recognizes the sensor fault and shuts down the engine. You might also notice that the engine starts but won’t respond to any throttle input before stalling.
#6. Sudden Acceleration or Engine Surging.
While less common than other symptoms, a failing accelerator pedal position sensor can sometimes cause sudden, unexpected acceleration or engine surging.
This dangerous condition occurs when the sensor sends erratic signals to the ECU, making the computer think you’re rapidly pressing and releasing the accelerator pedal.
A driver may experience sudden bursts of power while cruising at steady speeds, or the engine may surge while idling. This symptom is particularly concerning because it can lead to loss of vehicle control.
The surging may be intermittent, happening only when the sensor briefly malfunctions, or it could be constant if the sensor is sending consistently incorrect data to the engine control module.
#7. Acceleration Cuts Out at Highway Speeds.
The least common but most dangerous symptom is when acceleration suddenly cuts out while driving at highway speeds.
This happens when the APP sensor fails completely or sends conflicting signals that confuse the ECU, causing it to reduce or eliminate throttle response.
You’ll experience a sudden loss of power that can be terrifying when traveling at 60+ mph, especially when trying to pass or merge. The vehicle may feel like it’s coasting or like someone turned off the engine, though it typically continues running.
This intermittent loss of acceleration makes highway driving extremely hazardous. If you experience this symptom, it’s important to get off the highway safely and have the vehicle towed to a repair facility immediately.
Causes of a bad Accelerator Pedal position Sensor
- Damaged or corroded wiring of the accelerator sensor
- Bad or faulty sensor
- Contamination inside the accelerator sensor
- A bad connection between the PCM and the sensor
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.
#1. 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.
#2. 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.
#3. 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.
Diagnosing a Faulty Accelerator Pedal Position Sensor
Diagnosing a problem with the accelerator pedal position sensor typically involves a multi-step process:
- Visual Inspection: Start by visually inspecting the APP sensor and its wiring for any signs of damage, such as frayed cables, loose connections, or physical damage to the sensor itself.
- Diagnostic Trouble Codes: Use an OBD-II scanner to check for any diagnostic trouble codes related to the APP sensor. Common codes include P0122, P0123, P0222, and P0223.
- Sensor Output Testing: Measure the voltage output of the APP sensor while the accelerator pedal is being pressed and released. The readings should match the manufacturer’s specifications.
- Sensor Replacement: If the sensor is found to be faulty, replace it with a new, high-quality part. Be sure to follow the manufacturer’s instructions for proper installation and calibration.
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
- Screwdriver sets
- Safety glasses
- Voltmeter
- Work gloves
Needed parts
- Replacement accelerator pedal position sensor.
Let’s get started on the replacement process.
#1. 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.
#2. 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.
#3. 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.
#4. Remove the old APP sensor.
Gently pull out the old sensor and dispose of it properly. Ensure you don’t obstruct your local regulations.
#5. 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.
#6. Install the new APP sensor.
Following the reverse process, install the new sensor to where you removed the old one.
#7. 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.
#8. 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.
FAQs.
Q: 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.
Q: 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.
Q: 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.
Q: 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.
Conclusion
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.