Proper operation of your throttle position sensor is crucial to having an engine that runs and responds as it should do. However, incorrect TPS wiring is the most common electrical fault we come across! This page aims to explain how the TPS works and why just seeing the percentage moving between 0 and 100 doesn’t guarantee that you won’t have problems further down the line.
How does a TPS work? A TPS is a form of potentiometer, It has a resistive track and a wiper. A correctly wired TPS will have ground at one end of the resistive track and 5V at the other. The voltage potential along the track linearly increases from approx 0 to 5V. As the wiper moves along the track, the voltage at its terminal (terminal 2) will increase or decrease depending on whether it is closer to the 5V or ground terminal.
What happens if the TPS is wired incorrectly? Let’s imagine the 5V is applied to the wiper and the voltage measurement wire is connected to the track. Current will now be flowing through the wiper contact to the track. The wiper contact resistance forms a potential divide with the track resistance from the wiper to the ground terminal. The output voltage on the second wiper terminal that the ECU is measuring will still change as the wiper to ground resistance changes. So what’s the problem? There are two issues. The wiper contact resistance is not consistent and as this is now forming part of the potential divide circuit, any change in contact resistance resulting from changes in temperature, oxidation or even vibration can cause a change in the output voltage. This configuration also puts a significant current through the wiper contact, which generates heat and can cause the TPS to fail prematurely.
How can the correct wiring be determined?
- Measure the resistance between each pin combination with throttle closed
- Measure the resistance between each pin combination with the throttle open
- Use the spreadsheet below to determine which pin should be connected to which wire