I have a '98 BMW 740i and very often I'm getting "Transmission failsafe" on my dash and my car slows down or wont run. I have to turn it off until the dash shuts off in order for it to run again.

A lot of times it from a dying battery believe it our not, BMW's need proper voltage to operate correctly. Check your battery first, especially if it is 5 years or older. A faulty alternator or low trans fluid would also trip this fault.

Hello Israel1971, Tom is absolutely right. I had same thing happen to my 06. The problem was a cracked transmission sensor seal, allowing some tranny fluid to leak out. I didn't see any oil on my garage floor, but I did see it on the belly pan of the car. I did the same thing you are doing until it would not reset for me, and I had to have it towed to BMW service. They were able to replace the sensor and add fluid. It is a sealed transmission. You can't add fluid from the top like most other cars. It was just under $1100.00 at the dealer to have it repaired and they said that I hadn't hurt anything else. The car's system was protecting itself from more serious damage. I would say to get it into service before it leaves you stranded. Good luck, Rats

Thank you Tom and thank you Rats for your great advise. Will do!