# why is the initial reading of TPS on a meter is 5v instead of 0.5v, then decreases to 0.5v instead of 5v?

Hi, i want to know if my TPS is good or bad, i tested it the initial reading was 5v instead of 0.5v on the signal wire, on opening the throttle gas plate slowly, the voltage decreases instead of increas to the least 0.5v at WOT

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Lv 7
6 years ago

That's the way most resistive sensors work. They have a constant voltage on one wire, ground on another and the sense wire on a wiper between. You have the red meter lead on the pot wiper, which is close to the 5 volt source when the throttle is closed. As you open the throttle that wiper moves toward the ground lead, making the voltage decrease.

In other words, it's reading just what it should.

Analog meters are actually better for that. TPS type sensors don't usually quit completely. They get rough spots that mess up the reading. An analog meter lets you see how smoothly the sensor is working as you open the throttle.

• 6 years ago

This is how I check a TPS:

Unplug the connector from the TPS: Since I do not know the make, model, or year of the car, can't tell you the wire's color.

Start by measuring on one side of the three-wire plug. Turn the key to the ON position, but do not try to start the car. One wire should read close to 0 volts (or zero volts). This is typically one of the wires on the far-left or far-right of the plug.

Measure the middle connection, which is typically the signal wire. This should also read close to 0 volts.

Measure the final connection, which should be 5 volts and is our reference voltage. If you do not read 5 volts here, there is an issue with the sensor receiving power, and there is a potential short wire upstream from the plugIf this is the case, follow the wire to see if there is any physical damage.

It’s important to note that as long as you have 5 volts on one connection, and close to 0 volts on the other two, that your wires are OK. Know that the signal wire is commonly the middle connection, and note where the 5 volts and ground connections are.

Reconnect the wiring-harness connector and back-probe the sensor on signal and ground. If you are unsure how to back-probe a sensor. Do not "Poke" or "Piercing" onto or through the wires' insulation; you'll have problem later and it'll be harder to find.

Connect the positive (red) multimeter cable to the signal wire (the middle connection), and the ground (black) multimeter cable to the ground wire should have about 0.9 volts on the multimeter. Exact readings will vary on make and model.

Rotate the throttle body linkage and notice the change in voltage. If you are uncomfortable with rotating the linkage, that is not a problem. Simply rotate the multimeter on the windshield so you can see the readings from within the car and step on the gas pedal. It’s the same thing.

If the TPS is operating correctly, there should be a smooth transition from base voltage (in my case around 0.9 volts) to maximum voltage (approximately 4.47 volts). Rotate the linkage or press the gas pedal slowly, and look for voltage “spikes”. A spike would be a sudden and drastic change either to a high or low voltage.

For example, if you are half-way through pressing on the gas pedal and are reading about 2.5 volts, when a sudden spike goes to 4+ volts, or less than 1 volt, this would signal a faulty TPS sensor.

Here’s why: TPS sensors physically get worn out. If you see a section of the TPS that spikes each time you pass it (either on the way up or back down), there is a break in the connection because the physical resistive component has been worn away. This voltage spike is sent to the vehicles computer, and the computer processes the information as a sudden pressing of the gas pedal, or the sudden release of the gas pedal.

Hope it help.