# Allison 1000 Intermittent Temperature Readings



## HAMOP

I have an interesting one that maybe some of you have seen before.
01 GMC Sierra 2500 HD 8.1L with Allison 1000 5 spd.
Intermittent temp gauge readings. Usually only as transmission is warming up.
One morning I started the vehicle and within 10 seconds the warning came up that said Trans Temp Hot / Idle Engine.
Other times it does the same as I drive about 2 miles from home in the morning.
If I let trans warm up then shut off engine and start again sometimes it will register normal and other times the gauge will not register.
As this happens I will sometimes get an MIL and code 7000 & 7012.
Seems like a bad connection somewhere or bad temp sensor.
Where is the temp sensor?
I unplugged the 20 pin main wire harness from the back of the transmission and there was oil in the connectors.
I did the best I could to clean everything up and put it back together.
I will see if this solves the problem.


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## dbarton291

The transmission temperature sensor is in the transmission sump, the oil pan.
Here's the way I do something like this.  I would, when the hot warning comes on take one of those laser thermometers and get the temp off the line going from the transmission to the cooler.  That will tell you if the transmission really is overheating.
Then if you have access to a scanner that will read transmission temperature, see what the TCM is thinking the transmission temp is.  If you've got a reader saying the transmission sump is hot, like 300 degrees F, and the temp gun shows the temp is actually not overheating, you likely have a resistance problem between the temp sensor and the transmission control module.  Could be dirty connectors, possibly a failed transmission temp sensor (you replace it by replacing the internal harness inside the transmission), or (hopefully not) a problem with the TCM.


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## HAMOP

I was thinking i may have to replace the internal wiring harness due to the oil that I found within when I unplugged the 20 pin connector on the outside of the transmission. I don't think the transmission is that hot as it has even happened right after starting the vehicle and there is no way it got to that temp that quickly. I will pick up a thermal scanner so I can read line and pan temperature. I do have an OBDII code reader that will show live data. Will that information be there?
Thank you for the suggestions.


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## dbarton291

I don't think so.  You have to have the Allison DOC software to read the datastream.  It might read the OBD codes but I think that's it.  I've got an OTC Genisys scanner I use at home and it won't read the Allison stuff at all.  It has some heavy duty software package you have to buy to get the truck stuff but I don't think I'd ever use it.


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