Voltage for Coolant Temp Sensor

[deadeye]

Hey guys, I finnaly got a question for ya! Its for my 95 Talon TSi AWD 2.0 Turbo. I have mitchell one and its not as helpfull as it should be. Im trying to check some electrical stuff which is not my area of expertise or in my comfort zone.

I was wondering if anyone would know what the input voltage for a coolant temp sensor would be. I know its a 12 volt system but Im not sure if the computer sends 12 to the sensor or if its reduced to a smaller amount. I just want to make sure its getting power to the sensor, and then back to the computer. Im clueless to what its supposed to run at though.

The problem Im having is that im showing a coolant temp below threshold for closed loop fuel management code. I just happen to have a second car that is wrecked (it was perfect before some dink smashed into it while parked ) so I snagged the sensor out of it and threw it in the new car with no luck. I was going to put a new pigtail in but just wanted to be sure it was even getting power before I start cutting wires.

I also hooked up a Generic scanner and cleared the code and then did a little driving while plugged in. It showed that it was running at 195-210 on the scanner. I decided that I shouldnt be messing with it and driving so I turned it off and just a short time later the code popped back up. It also shows good coolant temp in the freeze frame for the code, so Im beginging to be a little stumped with this one. It still runs pretty good, but I know its running a little too rich (better than lean with a turbo). I just want to get it running right.

[Jeremy airjer W]

P0125?

[Scott K]

If it is a 5 volt reference at

212 degrees it should have .5v sensor should be at 2.07k ohms.

70 degrees should be 3 volts, sensor 37.3 k ohms

[deadeye]

Ya a P0125. After a while the P0170 pops up too, which is a fuel trim code due to the fact that its running rich.

Thanks for the voltage info. I figured it will be something different like that. I checked the ohms on the sensor at different temps and it was responding within range. For some reason I can find the ohm range in the books and Mitchel1 but not the voltage. I will dig a little more into it tommorow.

[Jeremy airjer W]

This is a step back into the past but if I remember right these use the O2 sensor to decide when to go into closed loop not the coolant temp. Monitor the O2 data and/or grab the one off the parts car and start with that. Its very possible the O2 is stuck rich, or there is an issue with the fuel system which is causing the O2 to remain rich. When the PCM sees the O2 switching it can start looking at other inputs and start its closed loop strategy.

[Jeremy airjer W]

For some reason I can find the ohm range in the books and Mitchel1 but not the voltage. I will dig a little more into it tommorow.

In the engine performance wiring diagrams it should list the reference voltage that the pcm provides.

[deadeye]

Will do, thanks for the info. It is entirely possible that the o2 is messed up.

When I got the car it was a real mess. The kid that crashed into my car got me this one as payment becasue he didnt have insurance, but whoever he got it from thought they were going to be on the Fast and the Furious or something. It has got lots of performance parts, but it was all done wrong. Boost controller hooked up wrong, vaccum lines going to the wrong spots or not hooked up, boost leaks, bad injectors, cam sensor ect. He had even hacked up the mass airflow sensor in hopes of getting a few extra hp. Its possible the O2 was damaged since it was being driven around with it hacked. It has been interesting getting it running to say the least and this seems to be the last hurdle before its going right.

You could say it has kept me out of trouble with all the time I have spent on it . It gives me something to do when Im not fishing, and has given me the chance to learn a lot too. I have pretty much just figured it out the old school way reading books, and with the help of my freinds so far.

Thanks again for the help so far, its really very much apreciated! I will post more as I figure it out.

[deadeye]

Well, I was able to finnaly find the spot on Mitchel1 that had the reference voltage info. Unfortunately I also found that it leaves out pin 92 on the ecm, which happens to be the one that im looking to check. At least I now know that I can check the continuity and resistance through the wires at the ecm connector eliminating a cut or grounded wire. One more step in the process of elimination.

[deadeye]

Well, a little update. I think I may have nailed it down now. Just for fun I typed the first code P0125 into mitchel1 and for that code it just says, "excessive time to enter closed loop". Nothing about the ECT sensor. So maybe the Manufacturer meaning of that code was different or something. So airjer, you were right on track with that call.

When doing the repair track the first thing it said to check was the O2 sensor. I just pulled it out and Im suprised that its even able to read anything. It was caked with soot. I remembered when I was working on getting it running it had a defective power transistor (the ignition control unit) and wasnt firing all the cylinders, but still pouring gas in. So hopefully that was the issue. Of course im parked in now so I guess I will know tommorow when I take it for a drive if its better.

Thanks again for the help.

[Jeremy airjer W]

Yup, thats what I was sayin.

[deadeye]

All clear on the western front! I took it out and beat on it a little today and no MIL so far. Its running much better. It idles nice and cruising it seems more leveled out. I thought it was quick before, with the proper air fuel mixture its really pulling hard at 17psi.

Muchos Gracias for the help!