I also have had the "Transmission Limited Function" exactly once. Came about 1000km into my ownership of an 89,000km car (private sale). I think rondeo is on the money, there are several different limp-home programs the computer may select, and the TLF message is a catch-all alert for all of them. In my case I had no gears, until I shut down and restarted the car, after which it seemed to be fine again. TLF itself doesn't create a permanent fault code it seems, it's up to whatever the underlying cause is as to whether you get a code logged and it stays in limp mode. I took the car to Ford within days but they found no fault codes stored (they did find software updates for the
PCM,
TCM &
ECU though).
Since then the car has behaved normally through a further 2000-ish km. The only issue is that sometimes it revs and lurches between first and second gear when in auto mode, like it momentarily selects the wrong gear or finds neutral. Not sure whether this represents an issue, or is part of normal operation.
My understanding of these gearboxes is, although they're marketed as an automatic, it's really a manual with computer-controlled shifts. It just happens the computer has also been programmed to shift automatically during driving for you. I'm inclined to think the computer is not infallible, and it can get confused and make a wrong shift at times. I've decided to try driving in manual mode for a while to see how it goes when I (partially) take over the decisions of when to shift for it. Also inclined to get an OBDII dongle to monitor in real time.