Your car’s accelerator pedal sensor translates the pressure you apply to the gas pedal into electronic signals that control the engine’s throttle. It tells your engine how fast you want to go.
When this sensor fails, it can disrupt the communication between the accelerator and the engine, leading to issues like sluggish acceleration, inconsistent performance, or even safety risks if the engine becomes unresponsive.

In this post, we’ll explore everything you need to know about accelerator pedal sensors, including how they work, the common symptoms of failure, how to diagnose the issue, and what to do if the sensor needs replacing. Let’s jump in!
What Does an Accelerator Pedal Sensor Do?
Common Symptoms of a Failing Accelerator Pedal Sensor
How to Diagnose a Bad Accelerator Pedal Sensor
How to Replace an Accelerator Pedal Sensor
What Does an Accelerator Pedal Sensor Do?
The accelerator pedal sensor (APS) is a key component in modern electronic throttle control (ETC) systems. It replaces the traditional throttle cable in older vehicles, allowing for smoother and more precise communication between the accelerator pedal and the engine.
The sensor’s job is to measure the position of the accelerator pedal and send electronic signals to the engine control module (ECM). The ECM then adjusts the throttle body to control the airflow into the engine, determining the car’s speed and acceleration.
The accelerator pedal sensor typically uses two internal sensors to ensure accuracy and reliability. If one sensor fails, the system relies on the backup to maintain safe operation, triggering an OBD fault code and placing the vehicle in “limp mode” to limit performance until the issue is resolved.
Without a functioning accelerator pedal sensor, the car may fail to respond correctly to your inputs, leading to sluggish acceleration, hesitation, or even loss of throttle control altogether.
Common Symptoms of a Failing Accelerator Pedal Sensor
A failing accelerator pedal sensor can cause noticeable performance issues. Here are the most common symptoms to watch for:
- Delayed or Sluggish Acceleration
When the sensor malfunctions, it may struggle to send accurate signals to the engine control module (ECM). This can result in delayed or sluggish responses when you press the gas pedal. - Unresponsive Pedal
In severe cases, the accelerator pedal may become completely unresponsive, preventing the car from accelerating or moving as intended. - Inconsistent Throttle Response
You may notice jerky acceleration, hesitation, or inconsistent engine power as the faulty sensor sends erratic signals to the ECM. - Check Engine Light
A failing accelerator pedal sensor can trigger the check engine light. Codes such as P2138 (Throttle/Pedal Position Sensor/Switch D/E Voltage Correlation) are commonly associated with this issue. - Reduced Power or Limp Mode
Many vehicles enter “limp mode” when the accelerator pedal sensor fails. In this mode, the car limits throttle response to protect the engine and transmission, allowing you to drive to a repair facility at reduced power. - Poor Fuel Efficiency
A malfunctioning sensor can disrupt the air-to-fuel ratio, causing the engine to work harder than necessary and reducing fuel efficiency.
If you experience any of these symptoms, it’s important to address the issue promptly. In the next section, we’ll discuss diagnosing a bad accelerator pedal sensor.
How to Diagnose a Bad Accelerator Pedal Sensor
Diagnosing a failing accelerator pedal sensor involves a combination of visual inspection, testing, and interpreting diagnostic trouble codes. Here’s a guide to pinpointing the issue:
1. Scan for Diagnostic Trouble Codes (DTCs)
Use an OBD-II scanner to check for error codes stored in the car’s engine control module (ECM). Common codes related to the accelerator pedal sensor include:
- P2122 – Throttle/Pedal Position Sensor/Switch “D” Circuit Low Input
Indicates that the sensor is sending a voltage signal lower than expected, possibly due to wiring issues or sensor failure. - P2127 – Throttle/Pedal Position Sensor/Switch “E” Circuit Low Input
Points to low voltage in the secondary circuit, often caused by internal sensor damage. - P2138 – Throttle/Pedal Position Sensor/Switch D/E Voltage Correlation
Suggests a mismatch between the two circuits of the sensor, indicating a potential fault in the sensor or its wiring.
2. Inspect the Accelerator Pedal Assembly
- Check the accelerator pedal and sensor for physical damage, corrosion, or loose connections.
- Examine the wiring harness and connectors for broken wires, frayed insulation, or corrosion.
3. Test the Accelerator Pedal Sensor
If you have a multimeter, you can test the sensor’s output voltage:
- Locate the terminals for the sensor’s circuits (refer to the vehicle’s service manual)
- With the ignition on (engine off), back probe the sensor with a graphing multimeter to measure voltage while pressing the accelerator pedal slowly downwards.
- The voltage graph should increase smoothly as the pedal is pressed. Erratic readings or no voltage change indicates a faulty sensor.
4. Perform a Throttle Position Check
Using a scan tool (scope), monitor the throttle position data while pressing the accelerator pedal. Look for:
- Smooth and consistent throttle position percentage increases.
- Discrepancies between the pedal position sensor and the throttle body readings indicate a sensor issue.
5. Confirm the Issue
If the sensor fails the tests or diagnostic codes point to a fault, the accelerator pedal sensor is likely the problem. Replace it with a new unit and verify the fix with a test drive.
In the next section, we’ll explain how to replace the accelerator pedal sensor.
How to Replace an Accelerator Pedal Sensor
Replacing an accelerator pedal sensor is a straightforward process for most vehicles. With the right tools and a bit of patience, you can get your car back to proper working order in jigtime. Here’s how:
1. Gather the Tools You’ll Need
- Socket set and ratchet.
- Screwdrivers (if required for your vehicle).
- Replacement accelerator pedal sensor (ensure it’s compatible with your make and model).
- Optional: OBD-II scanner to clear codes and confirm the fix.
2. Locate the Accelerator Pedal Sensor
- The sensor is typically integrated into the accelerator pedal assembly. Refer to your vehicle’s manual for its exact location.
- In most cases, it will be mounted near the firewall, connected to the pedal.
3. Remove the Accelerator Pedal Assembly
- Disconnect the electrical connector from the accelerator pedal sensor.
- Remove the bolts or screws securing the pedal assembly to the vehicle’s floor or firewall.
- Carefully take out the assembly to avoid damaging the wiring harness.
4. Replace the Sensor
- If the sensor is a separate component, remove it from the pedal assembly by unscrewing or unclipping it.
- Install the new sensor in its place, ensuring a secure fit. If the entire pedal assembly needs replacement, install the new unit.
5. Reinstall the Pedal Assembly
- Reattach the pedal assembly to its original position, securing it with bolts or screws.
- Reconnect the electrical connector to the new sensor.
6. Perform a Throttle Relearn Procedure (If Required)
- Use an OBD-II scanner to clear any stored diagnostic trouble codes. Verify that no new codes appear after replacement.
- Some vehicles may need a throttle relearn procedure to calibrate the new sensor.
- Follow the instructions in your vehicle’s manual or use a scan tool to initiate the relearn process.
Replacing the accelerator pedal sensor can resolve symptoms like poor acceleration, unresponsive throttle, and check engine light warnings. If the issue persists after replacement, further diagnosis of the throttle body or engine control module may be necessary.
Accelerator Pedal Sensor FAQs
1. Can a failing accelerator pedal sensor damage my engine?
While a faulty accelerator pedal sensor doesn’t directly harm the engine, it can cause inconsistent throttle responses, leading to rough performance and increased strain on components like the transmission. Prolonged issues can also reduce fuel efficiency and increase emissions.
2. How long does it take to replace an accelerator pedal sensor?
For most vehicles, replacing the accelerator pedal sensor takes about 30 minutes to an hour. The process is relatively simple if you have basic tools and follow the steps outlined in your vehicle’s manual.
3. What causes an accelerator pedal sensor to fail?
Common causes include:
- Wear and tear: Sensors degrade over time due to repeated use.
- Electrical issues: Corroded connectors, frayed wiring, or short circuits can disrupt the sensor’s function.
- Environmental factors: Exposure to moisture, heat, or debris can damage the sensor or its connections.
4. How much does it cost to replace an accelerator pedal sensor?
The cost varies depending on the make and model of your vehicle. On average:
- DIY replacement: $50–$200 for the sensor.
- Professional repair: $150–$400, including parts and labour.
5. Can I drive my car with a faulty accelerator pedal sensor?
Driving with a faulty accelerator pedal sensor isn’t recommended. While the car may still operate, symptoms like sluggish acceleration or limp mode can make driving unsafe and unpredictable. Address the issue promptly to avoid potential risks.
6. Do I need to calibrate a new accelerator pedal sensor?
Yes, many vehicles require a throttle relearn procedure to calibrate the new sensor. Some vehicles perform this automatically after a few driving cycles, while others may need a scan tool or specific steps outlined in the owner’s manual.
You may find the following pages helpful:
- About the Author
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John Cunningham is an Automotive Technician and writer on Rustyautos.com. He’s been a mechanic for over twenty-five years and has worked for GM, Volvo, Volkswagen, Land Rover, and Jaguar dealerships.
John uses his know-how and experience to write articles that help fellow gearheads with all aspects of vehicle ownership, including maintenance, repair, and troubleshooting.