Dear customer, the transmissions of these BMWs are electronic transmissions controlled by a module known as The TCM (transmission control module) which is an electronic module in charge of all transmission operation.
If the failure occurred unexpectedly, there were no power losses, there was no burning smell, there were no strange sounds, etc. It is very likely that the failure occurred at the electronic system level.
In this case, what we have to do is a computerized diagnosis, we need to examine the values of the live data stream of the transmission, an error code may have been generated, therefore a limp mode may be caused.
These transmissions have a limp mode when the computer receives an error code directly from the transmission that can mean a dangerous transmission failure or for the driver disables the speeds the vehicle enters a mode where it cannot be driven as a precaution.. It causes the gears of your transmission to be deactivated, the only way to correct this is by erasing the codes that may have been generated from the transmission through diagnostic equipment.
This is the most common thing that can happen dear customer, I do not think it is internal damage but simply an error code that could have generated the limp mode.
Then dear customer, if the error codes remain unverified according to the error code, for example, it may be a selector of the change selector that is clogged or may be that it does not allow the release of the gears.
Another common problem is that the brake sensor has been damaged, do a very simple test, verify that pressing the brake is activating the brake lights, and verify all fuses located under the dash and under the engine compartment, and that don't have any burned or loose.
Indicating that you have an internal transmission failure as such at the mechanical level is very difficult and i do not think so.