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Transmission failsafe occurs when the transmission senses a fault or is missing a needed input that is required for proper operation. Tansmission failsafe is not something that can just be reset - the underlying fault that is triggering failsafe must be fixed first.
Transmission failsafe can occur for many, many reasons. Anything from a simple low fluid level or failed sensor to complete transmission failure can cause failsafe. Even a missing input from the ABS
system or a faulty alternator / voltage problem can cause failsafe, etc, etc, etc.
The good news is that when failsafe occurs, the transmission computer logs a record of the fault, which can be read out to shed additional light on the exact nature of the issue. Thus, the only way to determine why the transmission is in failsafe is to have the fault memory read out using a BMW compatible scan tool. Once the fault memory is read, the problem can be identified, and the issue fixed.
Without knowing what faults are stored, all a person can do is guess at the problem - which can get very expensive, very quickly.
You can try to reset the transmission by turning the key to position 2 (all the way without starting the car or pressing the start/stop button twice with foot OFF the brake) and pushing the accelerator pedal to the floor for 2min. Again, the fault will likely return though until the underlying issue is addressed.
At this point, you can try the above as a temporary fix, but ultimately you will need to take the vehicle to a shop that has the proper equipment to read the fault memory and test volatges so that the issue can be determined.
There is no other way to resolve failsafe - the fault memory must first be read out so that the issue can be identified. Once the issue is identified, the problem can be corrected, the warning switched off, and normal transmission operation restored.
Sorry if you were hoping for a different answer, please don't shoot the messenger - I can only give the honest answer, which I have. Please remember that a low rating PUNISHES me for my honest and prompt response, and I receive nothing for my time and answer until a positive rating is clicked.
Please let me know if you have further questions. Please do not forget to click a positive rating as this is the only way I receive credit for my answer, thank you. Best wishes with your vehicle.