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The accelerator pedal position (APP) sensor on a diesel truck is a part that tracks the position of the accelerator pedal at any given time. When you depress the pedal, the APP sensor updates the electronic throttle control (ETC) about the new position.
When the APP sensor begins to fail, it can cause symptoms like a high idle, engaged limp mode, erratic acceleration, and a check engine light.
ProSource Diesel takes a look at the purpose of an accelerator pedal position sensor, the symptoms of a bad one, and how to test and reset it.
There are several potential reasons for APP sensor failure. A damaged sensor element is a common reason. This part has a wiper arm that keeps it clean, but the wiper arm can actually wear out the element by constant wiping.
Faulty cables are another reason for the APP sensor failing. The APP sensor is connected to the ETC with cables and the cables can corrode or fray, which destroys the connection.
A lack of voltage or a bad ground supply can also cause the APP sensor to fail. The accelerator pedal position sensor needs a steady power supply and good grounding to protect it against surges.
Finally, a bad electronic evaluation unit can make the power control module (PCM) think that the whole APP sensor is bad. When the sensor fails or is compromised, it will exhibit the symptoms in the next section.
In general, the accelerator pedal position sensor should last as long as your vehicle. However, it can fail due to a damaged sensor element or faulty cables. It can wear out early if it takes serious damage or is used heavily. Several distinct symptoms indicate impending failure.
– Check engine light comes on. This is due to the APP sensor sending incorrect readings or no readings to the ETC. This usually results in a bad air-fuel mixture, which will trigger the check engine light.
– Erratic engine response. If your engine suddenly starts speeding up or slowing down for no reason, then it might be the APP sensor. When sensors don’t agree, the result is usually reduced throttle action.
– High idle speed. If your accelerator pedal position sensor is going bad, it can trigger a higher engine idle speed. This is due to inaccurate readings that cause the ETC to increase the fuel supply. The extra fuel increases the idle RPM.
Testing the APP sensor usually involves checking the fault code. You can also visually inspect the sensor for signs of damage. For example, wear and tear from the wiper arm should be visible.
You can also check the various electrical connectors and cables for damage and wear. Use a multimeter to test if the sensor is working. This is generally a two-person job as someone has to carry out the test cycles while the other person monitors the results.
If you’ve determined that your APP sensor is bad, the first step is to buy a new APP sensor. The price of an APP sensor can vary depending on your vehicle and the engine. ProSource Diesel stocks a wide variety of accelerator pedal position sensors for different engines.
For example, an APP sensor for the 2002-2003 7.3-liter Ford Powerstroke engine costs $999. On the other hand, an accelerator pedal position sensor for the 2001-2005 6.6-liter Chevrolet Duramax LB7 and LLY only costs $59.
The method to replace your APP sensor will likely depend on your vehicle and engine.
In older models it is located in the engine bay near the throttle cable. Usually hidden underneath a protective cover that protects the throttle cable and assembly. (image on left below)
On trucks that do not have a throttle cable and instead have an electric throttle body (ETB), the sensor is typically located beneath or in your accelerator pedal assembly, which means you’ll need to remove that pedal to get at it. (image on right below)
After you locate the sensor, you can remove it and replace it with a new one. Or you could replace the entire pedal assembly if you have a newer truck.
APPS location on a 2001 Dodge on left (source) | APPS location on a 2002 Ford F250 on right (source)
If you replace your sensor and it needs to relearn the correct position, the following procedure is a general how-to.
Sometimes the APP sensor can be reset simply by disconnecting and reconnecting the battery. You can also do it by removing the fuse for your engine control module. In some cases, a reset might restore your sensor if it was simply the victim of a code error.
Whether you can clean the sensor or not depends on if it’s hermetically sealed into the housing. In some vehicles, the sensor is sealed and can’t be removed.
On sensors that aren’t sealed, a dirty coating can build up on the components.
To clean it, you should shut the engine off and step on the pedal hard at least 20 times. That should remove the coating and return your throttle response.
These two parts are somewhat similar, but the APP sensor detects the position and movement of the accelerator pedal and relays it to the ETC.
The throttle position sensor (TPS) monitors the position of the throttle plate and is positioned near the throttle body.
Another location for the TPS is in the accelerator pedal itself. In this case, the APPS is basically a TPS with a pedal attached. The APP is generally located beneath the accelerator pedal assembly.
Rely on ProSource Diesel for all your diesel truck parts needs. We stock a wide variety of replacement diesel parts as well as aftermarket upgrades, kits, and much more. ProSource is where the diesel repair shops shop for parts.
View our selection of Accelerator Pedal Position Sensors for your diesel truck here.
