I posted this a while back to clarify issues people were having with their FSS system.

The wrench is part of the Mercedes-Benz FSS system which is adaptive to your driving style and ambient conditions and time, it varies for everyone. The wrench will start appearing reminding you of upcoming service with the mileage left for that service showing next to the wrench. Example; when the wrench shows up with a reading of about 300 miles that means that in 300 miles service A will be needed.

If you buy your car new but its like an '04 model with low low miles like 1,000 and already requires service A, it is nothing more than that the FSS system also monitors the time the car has sat without use. So if your car has sat for a long time at a dealer prior to you purchasing it the system will also calculate that oil life sitting in your oil pan and countdown from the reset much faster.

Also the FSS system monitors your driving style and ambient conditions. If your driving style is aggressive you will see the countdown go suddenly from say 6,000 to maybe 5,300 in only 300 miles of driving. If you drive very conservatively then you will see the countdown parallel with the miles driven. Also if you live in a dusty climate it will also perform a faster countdown as opposed to a cleaner climate however the system will always calculate the time the oil has been there unchanged as well. In other words it has a life of its own when it tells you its due then its due.