This button allows a greater amount of differentiation in rotational speed between the front and rear tires. ASR takes its cue from the front wheels; how fast they're turning is approximately how fast the rears should be. However, when tires become clumped with snow, their rotational speed varies to such a degree that the ASR will actually keep you from moving. Same thing when they have chains on, if the chains load up with snow.

I've actually had this happen in a snowstorm; hitting the button allowed enough wheelspin to get me going again. In my case, the rear end just stepped out to one side, and the car allowed a sort of power slide...very controlled.

If it weren't for this feature, I'd have replaced the button with a defeat switch long ago. But then again, I know how to disable ASR when I want to

Hope this helps

__________________
"If God had meant for us to walk, why did he give us feet that fit car pedals?" Sir Sterling Moss

Michael
2014 E63S Estate
2006 SLK55
1995 E500
1986 Porsche 944 turbo