Q: Excessively high voltage in Throttle Position Sensor

asked by on October 27, 2016

My car is cranking but not starting, I lack a fuel pressure gauge so I was testing other, related stuff until I could get my hands on one. I got to the Throttle Position Sensor and started testing it. I started with the power supply. My repair guide says it should be about 5 volts, I got 5.1 so I figure that's pretty close so I chalked it up as good. Then I went to the ground return which my repair guide says it should be 12 volts. And I got 12 volts. So I chalk that up as good. Then I move on to what it's reading from the actual throttle position.

My repair guide says when closed (@ screw) should be 0.5 ~ 0.9v. I got an astonishing 25.7 volts. I had exposed a tiny portion of wiring so I could get my multimeter lead onto it (because it needs to be plugged in to read the throttle position) and I hooked the other end to my negative battery post. Did I do that wrong? (repair guide says to use an inline lead which I don't have) Or is that the actual reading? If so what does that mean?

My car has 185000 miles.
My car has an automatic transmission.

Car is not starting Inspection $79.99 - $89.99 Get a Quote

I’m not sure why you are getting such a high voltage, but you are making one mistake when checking TPS voltage. The ECM sends a 5 volt reference voltage to the TPS which passes through a variable resistor of the sensing circuit. This of course is connected to your throttle pedal. When the 5 volts passes through the resistor of the TPS, the voltage will vary based on the position of the throttle plate. This is how the ECM knows what you are doing with the gas pedal.

You can test a TPS in two ways, You can simply test the resistance with an Ohm meter or you can test the voltage change that occurs in the reference circuit. The mistake you are making is connecting the multimeter to the negative battery post. You need to connect one end to the 5 volt reference sent to the TPS from the ECM and the other lead to the center wire coming out out of the TPS. This is what they mean by inline. While doing this, with the key on, move the throttle plate and the voltage should change smoothly. It is the smooth change in voltage or resistance we are looking for. If it glitches, jumps or just doesn’t change, you need a new TPS.

To add, a TPS won’t make a car not start. You need to check the fuel pressure, check for spark and injector pulse.

If you should require further assistance, I recommend having the starting issue inspected by a qualified technician, such as one from YourMechanic.

Good luck!

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

What others are asking

Dash lights flashing on while driving

Hello, thank you for writing in. Electrical issues can be incredibly difficult to diagnose. Typically when every dash light turns on, there is an issue with the main power supply. This means an issue with the battery, alternator, wiring, or...

Engine stalls as I'm on the accelerator, but when I stop completely, it works just fine.1993 Honda Accord

Hi there. This can be caused by a number of things. If it only occurs when accelerating then I would check the fuel pressure first. If the fuel filter is old or clogged then this will occur. It can also...

Car won't accelerate when I press the gas pedal.

The lack of acceleration or starting may be caused by many different things, but may be a sign of a failing throttle position sensor. The throttle position sensor (TPS) is a sensor used to monitor the throttle position of the...

When I put the key in the ignition, all lights come on but it will not start.

There should be power available at the starter solenoid and it is grounded by it's mounting to the engine and there is a ground cable attached to one of the mounting bolts. When the key is turned, there should be...

Trying to pass emissions test. Failed once. Code P0449

Hello, thank you for writing in. Code P0449 will set when the system sees that the position of the vent valve, and the voltage for its position, do not match. There could be a wiring problem, a faulty hose, or...

Car won't start and the cd player ejected a cd without me touching it. What's going on?

Hi and thanks for contacting Your Mechanic. You had mentioned that your battery had 10.1 volts at the time and said that is what the battery usually has. A fully charged battery will have 12.6 volts, a 75% charged battery...

car trun dose not crank feel like it trying to frire but it dose not my rotar truns i check sark on 4 plugs getting gas

Hello, thank you for writing in. The testing you have done so far is great. If you know you have fuel pressure and spark then you can turn your attention to other possibilities. These include the air intake sensors like...

I changed the battery and now my windows go up and down by themselves and I have a clicking noise from the door

Hello, thank you for writing in. When these types of electrical issue occur after changing the battery, there may be several things you have to try to rectify the issue. One would be making sure the battery is hooked up...

Starting problems, starter failure - 1994 Suzuki Sidekick

Hello. Make sure you double check to see if the starter is getting good connections and the cables are good. You may just have a starter that is common to only last a few years before wearing out. Make sure...

Related articles

How to Clean Battery Connections
Cleaning your battery connections, especially if the terminals are corroded, will help ensure the battery lasts longer and performs well.
How Are Sensors Used to Improve a Car’s Performance?
Modern vehicles utilize a series of car sensors to improve performance and reduce emissions. The oxygen sensor helps reduce tailpipe emissions.
What Sensors Do All Cars Have? And What Optional Ones Are There?
Modern cars have an increasing amount of sensors. Most cars have an oxygen sensor and a throttle position sensor, but parking sensors are optional.