This article was updated in December 30, 2025 with new products and information by Mark S. Taylor
Common symptoms include a delayed response when pressing the gas, the car entering “limp mode,” and an illuminated Check Engine Light.
Does your car hesitate when you hit the gas, or feel like it has a “dead pedal”? These are classic symptoms of a bad accelerator pedal position sensor. This small electronic part tells your engine exactly how fast you want to go. When it fails, your car can become sluggish, unsafe, or stuck in a slow “limp mode.” As automotive experts, we know how scary it is when your car doesn’t listen to your foot. This guide explains the warning signs, the trouble codes you’ll see, and how to fix the problem safely.
Contents
What Is a Gas Pedal Sensor?
Your car has a part called the APP sensor. It is a key part. It watches how far you press the gas pedal. It then sends a sign to the car’s brain. The brain is the ECM. This system is new tech. It is called “drive-by-wire.” It uses wires, not a cable, to control the car’s speed.
How the Sensor Works
The sensor is an electronic part. It uses tech to see pedal position. It turns the pedal’s move into a sign. This sign tells the brain how much gas you want. The brain then uses this news. It sets the speed and the power of the car.
APP Sensor vs. TPS
Some people mix up the APP sensor and the TPS. They are not the same. The APP sensor is at the gas pedal. The TPS is on the engine. They work as a team. But they have different jobs. The APP reads your foot press. The TPS reads the engine’s throttle plate.
Where Is the Sensor?
You can find the sensor on the gas pedal. It is right above the pedal. In some cars, it is part of the pedal. Its spot can change. It depends on the car’s brand. But it is always by the driver’s feet.
8 Signs of a Bad APP Sensor
A bad sensor will cause clear issues. These problems change how your car drives. It is key to see these signs fast. Here are the eight most common signs of a bad sensor.
1. A Light Comes On (Most Common)
First, you may see a light. It is the check engine light. Your car’s brain sees a problem. The sensor sent bad news. So the light turns on. You might see other lights too. A tool can read the code. This tells you why it is on.
2. The Car Speeds Up in a Weird Way
A bad sensor can make the car act odd. You might feel a jerk or surge when you press the gas. There can also be a lag. It can feel like the car has a mind of its own. This is a clear sign. The sensor is not sending a good sign.
3. The Car Is Slow or Hesitates
You may feel a slow response. You press the gas, but not much happens. The car will feel like it is holding back. It takes more time to get up to speed. This lack of power is easy to see on a hill. Or when you get on the road.
4. The Car Idles Bad or Stalls
If the sensor sends a bad sign at rest, the car can’t idle well. You might see the car’s RPMs jump up and down. A normal idle is about 600-700 RPM. A bad sensor makes the fuel mix wrong. This can make your car stall at a red light.
5. The Car Goes into “Limp Mode”
Limp mode is a safety thing. The car uses it when it sees a big problem. The car’s power is cut down a lot. This is to stop more harm. Your top speed will be low. It is about 35-45 MPH. You will often see a note on the dash. It will say “Reduced Engine Power.”
6. The Gears Shift Bad
The car’s brain for the gears also gets news from the sensor. A bad sign can lead to bad shifts. You might feel a hard or late shift. The gears can feel like they slip. This is because they do not know the engine’s load.
7. You Use More Gas
Your car’s gas use can go down. The brain gets the wrong news from the sensor. This makes it give too much or too little fuel. This waste hurts your gas miles. In some cases, you may see black smoke from the back of the car.
8. The Car Won’t Go Past a Certain Speed
Sometimes, a bad sensor gets “stuck.” It gets stuck at one sign. This can make your car speed up fine. But then it hits a wall. It will not go past a set speed. This is true even if you press the pedal all the way down.
Codes for a Bad APP Sensor
When the sensor fails, it stores codes. A pro can read these codes with a tool. These codes help prove the problem. Here are the most common codes you will see.
P2135 – A/B Sensor Sign Mismatch
This is the most common code. It means the signs from two sensors do not match. Most APP sensors have two sensors. This is for safety. This code means their signs do not agree.
P2138 – D/E Sensor Sign Mismatch
This code is a lot like P2135. It points to a different circuit in the same part. It often shows up with P2135. Seeing both codes is strong proof. It means the sensor is bad.
P0120 – A Sensor Circuit Problem
This code can mean the APP sensor is bad. Or the TPS is bad. It points to a circuit problem. It could also be bad wires. More work is needed to find the real cause.
Other Codes
You may also see other codes. Like P2121, P2122, P2123, P2127, and P2128. All of these are for the sensor circuits. They show a specific electrical problem in the sensor or its wires.
Why Do These Sensors Fail?
These sensors can fail for a few reasons. Like any part, they wear out. Here are the most common causes.
- Wear from use: The sensor moves. So it just wears out in time.
- Power problems: Bad plugs or rusty wires are a big cause.
- Low power: A bad ground or power feed can make it fail.
- Harm to the part: Harm to the pedal can harm the sensor.
- Water or spills: Water or spills in the footwell can harm the part.
How to Find a Bad APP Sensor
Finding a bad sensor is a step-by-step job. You can do some of these checks. For others, you may need a pro. Follow these steps to find the issue.
Step 1 – Note the Signs
First, note all the signs you feel. When do they happen? Does it happen when the car is cold? The signs can come and go. So good notes are a big help.
Step 2 – Read the Codes
The best way to start is with a code tool. You can buy a basic tool for not much money. Read the codes from the car’s brain. Look for codes like P2135 or P2138. Write down all the codes you see.
Step 3 – Look at the Part
Look at the wires to the sensor. Check for harm or rust. Look at the pedal for harm. Make sure the plug is tight and not loose.
Step 4 – Test with a Tool (Advanced)
This step takes some skill. You can use a tool to check the sensor’s power feed. It is usually 5 volts. You can also test the sign as you press the pedal. You will need a car book for the right info.
Step 5 – Get a Pro to Check
If you are not sure, see a pro. A pro can test the sensor with a better tool. This tool checks the real sign vs. the hoped-for sign. They can also rule out wire problems. They can prove the part is bad.
Can You Drive with a Bad Sensor?
Driving with a bad sensor is not a good idea. It can be unsafe. But in a crisis, you might be able to drive a short way. Here is what you need to know.
Short Trips Only (In a Crisis)
If your car is in limp mode, you can often drive it to a safe spot. The low power lets you get off the road. Your top speed will be low. Stay off the main roads.
The Risks
Odd speed changes are very unsafe. You could lose power at a bad time. Like in the middle of traffic. The car could also stall. This raises your crash risk.
When to Stop Now
You should stop driving right away. Do this if the gas pedal does nothing. If the car speeds up on its own, stop. If it stalls a lot in traffic, pull over. Get help.
What It Costs to Fix the Sensor
Fixing this part is a common job. The cost is often fair. Here is a simple look at the cost for parts and work.
| Cost Type | Price |
|---|---|
| Parts Cost | $50 – $200 |
| Work Cost | $40 – $300 |
| Total Cost | $100 – $450 |
The part cost depends on your car. A sensor alone can be $30-$100. But many cars need the whole pedal. The work cost depends on how hard the sensor is to get to.
How to Fix the Sensor (A Quick Look)
Fixing the sensor is often an easy job. For many cars, you can do it yourself. Here is a fast look at how it’s done.
Tools You Need
You will need a few tools. A code tool is needed to clear codes. A tool set with sockets or screwdrivers is usually all you need. The job often takes just 10 to 15 minutes.
The Basic Steps
First, take the battery cable off. This is for safety. You might need to take a panel off to see the pedal. Unplug the wire from the sensor. Take the bolts off. There are usually just a few. Put the new part on. Plug it back in. Test it. Some cars may need a pro to set the brain.
When to Get a Pro
You should see a pro if the new part needs to be set. If the pedal is hard to get to, a pro is a good choice. If you see many codes, it may mean a wire problem. That needs a pro’s touch.
APP Sensor vs. TPS: Know the Difference
It is key to know the difference between these two parts. Their names are alike. Their jobs are related. But they are not the same. Knowing the difference helps with the fix.
| Feature | APP Sensor | TPS (Throttle Position Sensor) |
|---|---|---|
| Where it is | At the gas pedal. | On the engine. |
| What it does | Reads pedal press. | Reads throttle plate. |
| Bad signs | Lag, limp mode. | A lot like the APP sensor. |
| Fix | Often part of the pedal. | A part on the engine. |
Both parts send news to the car’s brain. The brain checks the signs to make sure they match. Many of their bad signs are the same. Codes are the best way to tell which one is bad.
FAQ About Bad Accelerator Pedal Position Sensor
Q: How do you reset the accelerator pedal position sensor?
A: You can try to reset the gas pedal sensor. Unhook the car battery. Wait a few minutes. This can clear the car’s memory. It may fix the sensor problem.
Q: How much does it cost to replace an accelerator pedal sensor?
A: To fix a gas pedal sensor, it costs $100 to $450. This cost is for the part and the work. The final price can vary by car.
Q: What are the symptoms of a bad accelerator pedal position sensor?
A: A bad gas pedal sensor has signs. The check engine light may turn on. The car can lag or feel slow. It might go into limp mode. The car can also idle rough.
Q: What does the accelerator pedal position sensor do?
A: The gas pedal sensor tells the car’s brain one thing. It tells it how far down you press the gas. The brain then sets the engine’s speed and power.
Q: How long does an accelerator pedal position sensor last?
A: A gas pedal sensor can last a long time. It has no set life span. It can fail fast. This is due to a power or harm flaw.
The Bottom Line: Do Not Ignore the Signs
The sensor is a key part for your gas pedal. Ignoring its signs can be unsafe. A light on the dash plus bad speed up means the sensor is likely bad. Codes P2135 and P2138 prove this. The fix can cost $150-$450. But it is an easy fix. It stops unsafe times. Read the codes if you see signs. Get a pro to check if you are not sure. Fix the part fast for your safety.
Quick Summary
- A light on the dash is a top sign.
- Lag, slow speed, and limp mode are key signs.
- Codes P2135 and P2138 point to the sensor.
- The part can fail from wear, power issues, or harm.
- The fix cost is often $100 to $450.
- You can drive a short way in limp mode, but it is not safe.
- Knowing the APP sensor from the TPS is key to a right fix.