The days of having to constantly adjust the throttle cable due to a loose nut on the carburetor are long gone. Today's modern cars, trucks, and SUVs are all equipped with an electronic throttle control system that contains an accelerator pedal position (APP) sensor. This sensor's primary job is to monitor the position of the throttle pedal and send an electronic signal to open the throttle body as you depress the gas pedal. Although this device often lasts the entire lifespan of your vehicle, there are occasions when it will fail, wear out or need to be replaced.

The APP sensor essentially tells your engine how fast or slow to drive as you press the gas pedal. When you press down or lift off the throttle, it sends an electrical signal to the vehicle’s ECU or ECM as it's also referred to, and then transmits that signal to the fuel system. The primary reason why this part would fail is due to exposure to high heat as it's typically located on the floorboard and next to the firewall of the vehicle. Unfortunately, this part can't be repaired, so when a certified mechanic diagnoses that there is a problem with this device, you'll have to replace the accelerator pedal position sensor.

Like most components on the vehicle, a bad or failing APP sensor will display a few warning symptoms including triggering error codes, warning lights and a few physical symptoms that should alert the driver that a problem exists. Listed below are a few of these warning signs.

1. Engine throttle is inconsistent

When you press down on the gas pedal, your engine should respond directly and instantly. However, when a problem with the APP sensor exists, the vehicle's ability to consistently accelerate or decelerate as directed by the driver will be reduced. This could cause a serious safety situation as essentially the driver is not in control of the vehicle. When this occurs, you should pull your vehicle to a safe place off the road and contact a mechanic as soon as possible to inspect the reason why throttle control is not consistent.

2. Engine does not run efficiently

When the APP sensor is not functioning properly, it will also have problems with fuel efficiency. Besides monitoring and applying throttle pressure to the throttle body, it also helps to stabilize the throttle control. It's designed to take input from the driver, but steady the application of fuel pressure as it relays the information from the ECU to the throttle body of the vehicle. If the sensor is not able to transmit this information to the ECU correctly due to a loose wire, being worn out or have broken entirely, you'll notice a huge difference in fuel economy.

3. Check Engine Light comes on

Since the APP sensor is monitored by the ECU, it is one of those components that will trigger an error code in the ECU when an issue is discovered. This will signal the Check Engine Light to illuminate on the dashboard. Anytime this light is on, you should take it seriously as there are multiple components that will trigger this warning light. Contact a local ASE certified mechanic if the Check Engine Light comes on so they can properly diagnose the problem and correct it quickly. In order to work properly, all of the sensors inside your car must function at 100 percent efficiency.

When one fails, it can impact the operation of the entire vehicle. Anytime you notice any of the above symptoms or warning signs, you should contact a local ASE certified mechanic through YourMechanic. Our professional and experienced automotive technicians can travel to your home or workplace to complete diagnostic inspections and repairs of virtually any mechanical or electrical problem with your vehicle – including replacing the APP sensor.

This article originally appeared on YourMechanic.com as Symptoms of a Bad or Failing Throttle/Accelerator Pedal Position Sensor and was authored by Timothy Charlet.


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