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Transmission overheat trouble

I know it’s a stretch but if you leave the trans connector disconnected and read the data live on that sensor does it read the same value?

Trick is to find out what the ohm resistance is for a good sensor then fool the ecm by placing a resistor or a potentiometer on those pins of the trans connector. Verify live data again for acceptable readings. That will verify the harness and ecm/tcm is functioning properly pointing the issue to within the transmission.
 
Do the ohms resistance test on that transmission temperature sensor.
Requires warming the sensor and reading the ohms scale as its heating.
Candy or meat thermometer and a pan of water on the burner with the sensor in the water is the test means.
 
I got the resistance vs temp chart today and tested the old parts. The manifold tested to specs, the continuity of the two pins tested good, and after plugging the harness into the manifold there was no significant difference. 4.9 K as apposed as 4.7 k. I'll try to get into the back of the trans and test the new parts I installed.
 
I am trying to locate a detailed wiring schematic of the transmission temperature circuit. Does anyone know of a web site to download one or does someone have one they can post? I’ve been looking for manufacture shop manuals but they are pricy.
 
Searching online for the GM service manual would be the way to go, but you should also be able to stop by a local GM dealer at the parts counter and ask for it. most of the time they keep a library where you can scan off copies of what you need or they can print them for you. Service department might frown but the parts guys don't care LOL
 
Ive tested: At the TCM J2 red connector, pin 10 yel/blk 4.9 v, pin 31 bro 12v, 20 pin connector engine side, pin G ground, pin H 5 v. 20 pin connector, trans side leads between pin G and H, 44k ohmes @ 59 deg F (scanner reading), ran engine ohmes steady decreased as temperature raised. 2.721k ohmes @ 77 deg F (scanner reading.)

I’m thinking my problems is a wiring problem between the TCM and ECM, or ECM to gauge or the gauge itself. I am still working on the ground connectors.
 
It will be interesting what you can find out. You should have a dedicated hot and a ground going back to the computer. The funny thing is the that the TFT sensor is a Negative Temperature Coefficient thermistor. The hotter the transmission fluid gets the lower the resistance.
 
Did you consider that you might have a short somewhere causing the computer to think that the transmission is overheating? If more (TFT) voltage is leaving the TCM I would believe that it would be fooling the computer. Do yourself a favor and reconsider your leanings on replacing internal electrical components. A parts cannon is not good.
 
I don't know where the data is read from at the TCM whether it is the positive side or the negative side of the Transmission Fluid Temp sensor. I would first suspect that you have a short in the TFT circuit. Consider taking a resistance reading of the TFT, an Ohms reading through the TFT and match it up with a temperature chart. A negative to the transmission case Ohms check. I would also check for resistance or continuity at the TFT to every other circuit feeding in and back out of the transmission. If everything checks out at the transmission then you should work backwards back to the TCM.
 
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