Since finding anything relating to the diesel before 2013 in the US is near impossible, even the WSM for 11-13 is vague I dug in my bookmarks and found this handy bit on the W5A580/NAG1 gearbox which is what the diesels have.... to confirm check the tag on the box.... Its a very informative manual on the box so have a dig in it, you may not find where the TCMA is located but may find a fix for the problem... On the WG the TransControlModule was under the console next to the shifter.
Link will download a pdf file.............
I suppose you have checked the engine coolant sensor as that's the lost signal, but in saying that there is a brain, (circuit board, conductor plate) in the W5A580 gearbox, on the valve body which suffers failures. You have to have the Jeep one as there is extra connections that Mercedes didn't have.
As Farwest said contact All Grand Cherokee in Melbourne, you are pretty much wasting your time with anyone else
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