"Failsafe" programs are a running mode which allow something to keep going when the normal operating mode is not available. As it applies to the engine failsafe, this usually means that the computer is getting an input from a sensor which is not consistent with the ability to run, so the computer is ignoring that input and substituting a stock value in order to keep the engine running until you can get help. It is considered a "limp-home" mode and a signal that you need to have the car checked by a competent mechanic who can diagnose the problem. I have no idea what could cause this, I'm sure the list of possiblilities is long. Last winter, on a day when it was about 20 degrees below, my transmission went into failsafe mode. In that mode, I was able to get home and park it inside, but I was stuck in 5th gear and the transmission would not shift into any other gear even at a full stop. The next day it started and ran normally. I took it into my mechanic, and the computer had stored a code indicating that the gear shift indicator signal was not consistent with any normal value. My mechanic told me that in his experience often the plug to the gear shift position indicator will make a poor connection in extremely cold weather, and suggested leaving it alone and seeing if the problem occured again. I've driven the car about 12000 miles since with no more difficulty. This is an example of the transmission computer receiving a bad signal, and placing the transmission in "limp-home mode" i.e. staying in Drive, rather than stranding me by the road. If you are going into fail-safe mode on a repeated basis, I would be thinking about a bad sensor or an intermittent electrical fault. The place to start is reading codes from the computer. I note that your posting is a couple of months old. Any follow-up on what has happened since?
