Throttle position sensor signal wire producing voltage

Background: Check engine light indicated a problem with the throttle position sensor (unfortunately, don’t have the exact code). The TPS on my model ('96 Dodge Intrepid 3.3L) is the non-adjustable type. There are three wires going to the TPS – a power source, a signal wire, and a ground. The TPS acts as a potentiometer and depending on the throttle position, sends a voltage signal down the signal wire to the computer.

Here’s my question/issue: After disconnecting the TPS, I tested the three wires with a multimeter. Power source (5V) and ground were fine. But I’m getting a voltage reading of about 4.35V on the signal wire. It’s my understanding that with the TPS disconnected, I shouldn’t be getting any voltage on that wire. Does that sound correct? If so, what would be causing me to get a voltage reading there? I’m assuming some type of problems with the wires, maybe an exposed wire on the signal wire somewhere?

As a note, here’s a youtube video that’s basically doing the same thing I just did (from 1:35 to 1:55):

Notice on his middle wire, he’s getting a reading of 0.01V. I’m getting a reading of 4.35V. Trying to figure out what would cause this difference.

Just tested it again. Seems that the position and the angle that I hold the connector (not the leads) causes the voltage to jump from very low to 4.15V (OP should also say 4.15V, not 4.35V). Does this seem to indicate there’s a problem with the wiring at the connector? And that turning or twisting the connector is causing wires to touch?

It appears you have a problem with the connector since you say that you see voltage on the sense lead when you move the connector. To verify it you could disconnect the battery power or the connection going to the ECU and check the resistance across those leads as you move the connector around. If you get high and low resistance readings then you have proved the crossed connection between the wires.

With the battery disconnected, depending on how I move the connector, I can get a resistance reading on all three combinations of signal/power, signal/ground, and power/ground. Wasn’t sure which pair you meant, so I tried all 3 (electrical circuits aren’t my strong point). So it looks like one of those is a bad sign?

You need the load of the TPS to stabilize the signel line. By reading the signel line voltage from the plug alone you are reading the input to the Analog to Digital converter. Do what R & W did, back probe the connector while it is attached to the TPS. Not only will you be able to determine what the A/D is seeing in real life but also the operation of the TPS as you open the throttle. Look for that smooth transistion that is not affected by vibration. Also move the wire harness around to see if the signel voltage jumps.

Let us know the results of your testing.

Concur w/ @researcher above … the experiment you are doing won’t produce reliable results, as you are attempting to measure the input of a circuit on the ECM, with nothing providing a voltage to that input. Circuits like that are called “floating” inputs, b/c without a source voltage they could measure most anything. In other words, that measurement is meaningless, and could well depend on how the wires are bent, how you hold onto them, as that would change the capacitance between the wires.

With the TPS connected, then that input to the ECM should do what it is supposed to do, vary in the range of 0 volts to 5 volts as the throttle is moved. “Back probing” means to probe the connector from behind with a thin probe. Sometimes I use one of those pins that come with new shirts, those fit in tight spots. Other times the DVM probes themselves are thin enough. Just depends. Back-probing gives you access to the metallic pin, that would can’t access from where the two connectors mate.

The other option is to puncture the wire insulation, but that’s not as desirable as you end up w/a punctured wire that might allow moisture and corrode.

Edit: I had to test my TPS on my Corolla one time, and the way I did it was remove the TPS and test it by itself, on the bench. I connected up 5 volts from a power supply to the 5 volt pin, ground to the other. the Corolla’s TPS isn’t a variable resistor though, it is just a switch that indicates either “idle” or “wide open”. So doing a bench measurement on yours might not be as simple.