I would also clean your MAF sensor. My X has a history of Trans Failsafe Prog messages, which sometimes just put the tranny in limp mode, and sometimes actually kills the engine. It's lots of fun to try and steer an X5, with impending traffic furniture coming up or another car, without a power steering pump!

Anyways, after years with the issue, and help from this very board, I've determined that 100% of the time its a dirty MAF sensor, which is then interpreted by the ECU to trigger the TRANS FAILSAFE PROG dash message, and sometimes even shut the engine down. I've always pictured a German engineer on the team saying (in your best German accent), "Hey, let's prrrograam ze ECU to shaat down ze engine ven ze zimple leetle air flow zensor is just duurty". haha.. (My wife is German, so I can tease a bit, no?).

MAF stands for Mass Air Flow, and its a 4" diameter plastic tube with two metal cross hairs inside, plus a electrical connector on the outside of the tube. Its mounted in between the air filter box (air intake for the car), and the engine's air intake snout, all inline / part of the air intake plastic plenum (piping/tube). Its super easy to remove and replace. The metal cross hairs sense moisture levels, temp and other things from the air traveling into the engine, and the ECU monitors this and adjusts the engine's fuel, air, and spark advance to compensate for changing environmental conditions. The metal on the cross hairs is some type of rare earth mineral... so.. it's therefore ultra sensitive to getting dirty and altering the readings. Most mechanics will just replace them (but they're fairly expensive), or, you can just try cleaning the cross hairs.

I suggest pulling the MAF sensor (out of the car, don't just disconnect some), and heavily spray it with Hexane. You can buy Hexane at any auto parts store. It may even say, "MAF Sensor Cleaner" on it. Don't touch the cross hairs, and don't use anything else to clean them. Don't just spray it once. I tried that, and it doesn't really clean it enough. You basically have to expend 1/2 of a can of Hexane spray on it. It will be dripping heavily onto the ground. Keep spraying off and on. Reinstall.

All 7 times I've had the TRANS FAILSAFE issue, replacing or cleaning the MAF immediately resolved the problem, and it doesn't come back for 30k to 40k miles.

It might be what the guys are saying too. (I'm keeping this thread for that info. Great, detailed auto trans information I did not know!). I'm only saying, try the MAF sensor cleaning too, just in case, and it will only cost you $7.95. If the cleaning doesn't work, I'd also consider replacing the MAF. They don't always clean up perfectly.