How can I check the voltage on a TPS if it's not plugged in

[happydog500]

My 97 started to act up again. After a few weeks running good, it quit last night and today when I drive it down the street with my foot off the pedel, it goes down the road at 35mph.

Before I buy a TPS, I want to check the volts to make sure that's the problem. I'm at my friends garage and we don't understand one part.

The instructions say to check the voltage at the TPS. The only way to get to the wires is to unplug it. With it unplugged, there's no volts.

How are we suppoised to get a volt reading when there is no volts?

[HotZ28]

I usually use a needle (used to sew with) and probe the wire through the insulation. You can then place the ground (black) probe of the DVOM to any ground (does not have to be the other TPS black wire) and the other (red) wire of the DVOM to the needle. Some people strip back a small portion of the insulation on the BLUE wire on the TPS harness and probe the exposed wire.

Have you checked the spring return on the TPS? The lever on the TPS should move back and forth with the movement of the throttle body. Another way to check this is to place your finger on the little lever on the TPS, then move it to the open position without moving the TB. You should be able to see if it has a spring return, back to the original position. I have seen several TPS with a broken spring lately!

[happydog500]

Yes, we checked the spring last night. Everything works good.

After the car gets a code and gets a default value it seems to drive good. Without checking it may not get the mileage it's used to tho.

I think I liked it better when we had cables

[Bassasasin]

Does sound like a TPS.... I dont think they are too hard to replace.
If your inclined to take it off and clean it and it would work for a while, but you would have to invest in a cleaner and truthfully just getting another one may be the end result anyway. I pick them up at the boneyard and have one around to use to check it with.
There may be a checkout for it to check it in OHMS out of the circuit. I think it runs 2000 to 10000 ohms. Basically to see if it returns to the same value and smoothly changes its value as you turn the potentiometer (POT) or release the throttle. I also would expect it to fail in the range that is used most often like the lower end of the POT.

Just as note: Checking it with a sharp point isn't recommended by the manufacrurer since it degrades the insulation but I would do it anyway as long as you repair or barely pierce it.

The PCM would establish a read of the range it sees if you disconnected the battery but if it is bad it keeps getting new results from the dirt or whatever in the potentiometer (variable resistor) in the TPS sensor changing it irratically.

Just in thinking as for the mileage. If you have to brake to slow it down your burning off energy in the brakes and gas. If you were on the highway I wouldnt expect too much bad gas mileage.


Good Luck

[HotZ28]

I guess in my previous post, I assumed that you did not have access to a scanner capable of reading live data. If you do have access to such a scanner, you can check the TPS voltage, or % throttle opening with that. (Some scanners read % and others read voltage). A scanner is the preferred method, and what I have been using for many years. Back in the mid 80’s, we did not have that luxury and had to probe the wire and use a DVOM!

A new TPS only cost about 47 bucks and takes 15 min to install! You may need an offset screwdriver!