The throttle position sensor is part of your vehicle fuel management system that helps ensure your engine is getting the right mixture of fuel and air at every moment. The throttle position sensor provides the most direct signal to the fuel injection system of what power demands are being made of the engine. The TPS signal is measured and combined many times per second with other data such as air temperature, engine RPM, (actual) air mass flow, and how quickly the throttle position may be changing. These data determine precisely how much fuel to inject into the engine for the next few milliseconds. This is done repeatedly, many times per second. If the throttle position sensor and its other sensor partners do their job correctly, your car accelerates, cruises, or coasts down smoothly and efficiently, as you expect.
The throttle position sensor can fail in several ways, all of which result in poor fuel performance at best, and performance limitations that may create safety hazard for you and other motorists at worst. This sensor can fail gradually, or all at once. In most cases, the Check Engine Light is illuminated if a TPS failure is detected. Also, most manufacturers provide a “limp home” mode of operation with reduced power if a failure is detected. This would at least allow getting off a busy highway in a safer manner. Once the TPS begins to fail, even partially, you’ll need to replace it right away. Replacing the TPS will include clearing relevant fault codes, and may require software re-programming of the new TPS module to match other engine management software. This is all best left to a professional mechanic who can provide you with a diagnosis, and then install the correct replacement part.
Here are some common symptoms of a bad or failing throttle position sensor to watch for:
1. Car won’t accelerate or lacks power when accelerating
It may feel as though the car just doesn't accelerate as it should. It may accelerate smoothly, but lack power. On the flip side, it may be that your car suddenly speeds up while you’re driving, even if you haven’t pressed the accelerator. If these symptoms occur, there's a good chance you've got a problem with the throttle position sensor.
2. Engine won’t idle smoothly, idles too slow, or stalls
If you start to experience engine misfires, stalling, rough idling, or poor running at a stop light, these can also be warning signs of a failing throttle position sensor. You don't want to wait to get this checked out!
3. Car accelerates, but won’t exceed a relatively low speed (20-30 mph) or shift up
This is another failure mode of the TPS, which indicates that it is falsely limiting the power being requested with your accelerator pedal foot. This symptom often goes hand in hand with lack-of-power behavior.
4. Check Engine Light comes on, accompanied by any of the above behaviors
The Check Engine Light may come on if you’re having issues with your throttle position sensor. This isn’t always the case though, so don’t wait for this to happen before you get it checked out. If you have any of the above symptoms, have your vehicle checked for trouble codes to make sure that is the problem.
The throttle position sensor is key to getting the desired power and fuel efficiency from your vehicle in any driving situation. As the symptoms listed above make clear, failure of this component has serious safety implications, and must be checked out immediately by a qualified mechanic.