Limp home mode is not just on our M5's but applies to most OBDII model vehicles. Limp home mode generally sets the check engine light and the DME ( BMW ) or PCM simulates the valves of the failed sensor to get you home. This does not apply to all sensors. Some failure will cause a no start situtation that is out of control of the PCM. It is there to serve two purposes, one to allow you to get home or to a repair facility and second, to protect the engine. In some cases it will retard the drivability of the vehicle. The check engine like will go on and if it is flashing, it is letting you know that damage is being done to the catalytic converter. Hope this answers your question.