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My Tranny THINKS It's Getting Hot.

Merlin

Merlin

New member
I rebuilt my transmission a few months ago and I had an issue with it heating up to what it said was 290* I had a local transmission place look at it and they thought it was a bad sensor and so they replaced my harness and temp sensor in the transmission and sent it on its way. The fluid wasn't burnt, nor was the temperature ever as indicated. Tested it with an infrared temp sensor and the temp was a cool 180*ish.

The other day i took a 1.5 hr trip and on the highway, it kicked me out of fourth gear, which is an indication that it has overtemped. i got home and the temp via HPT read 260*, but the temp of the pan was 165* via the IR and the fluid temp off of the stick was 180*. I also saw no indication of bubbling on the fluid.

Does anyone have a good explanation of what is going on and is there anyway to eliminate the fourth gear lockout (temporarily) until i can get this issue sorted? I have talked to, but have yet gone to the shop again to get this issue re-diagnosed. I have a long trip i will be on soon and I cannot be held up by a fourth gear lockout again.


CLIFFNOTES: My tranny thinks its heating up, but it is only at 180*. anyone have an idea why?
 


The temp sensors in these transmissions dont often fail but I have seen a few odd electrical problems cause this. First I would check the grounds and the connector on the trans and pcm to make sure everything is clean and there is no corrosion. The trans temp sensor resistance will drop when it gets warmer. A friend of mine ran into this when swapping pcms in his car and he know good and well the trans temp was fine before he changed pcms so he verified the temp just as you did to know that the pcm reading was incorrect and then added a resistor in line of the temp sensor wire and then the pcm read correctly. Did you have this problem at all before you rebuilt the trans? Was anything other than the trans rebuild done during any of this such as a different pcm or wiring or anything?
 
I rebuilt a different transmission and put it into my car. my car is a 00 and I think that the tranny that i put in there was a 2001. They had an issue with it happening and they changed the sensor, but If both sensors arent compatable (thye have a different resistance temp value) then if they took and got the same part numbed, then this could be the cause.



To answer your question, this issue was not present when i first swapped transmissions and the only electrical things i unplugged on the first swap was the transmission connector. I doubt that there are any issues with grounds (unless i missed one, but i think that the trans shop would have caught that) and there were no swaps of pcm's or anything
 
The temp sensors are the same, you can put a newer trans in an older car and it wouldnt effect the temp reading. You could also check the resistance of the sensor after the trans is warmed up and post up what it reads. On the Info page on my website I have resistance valves at a few various temps, 190 is the high end of this and has the valves there so you can use that to compare.
 
you have a suggestion on what is the best way to go around testing the resistance of the sensor? get it warmed up and then shut the car off and unplug the trans? meeasure from the plug?

J
 


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