Hi,

Does anyone know how the diff / traction control works?

Seems very effective on slippery stuff at getting power down rather than just backing off the engine and chugging like systems of old.

Drives more like a Torsen diff for those of us old enough to remember but assume it's just electronics and not mechanical cleverness?

It's a Haldex system. I think I found it on Youtube or somewhere similar a year or so back. Something about shifting power via the rear diff AWD system clutches to more front-rear as required and using the brakes as well?

I just have FWD

Combination of power and using the ABS then would be my guess. My cars are all AWD and I've no recent experience of 2WD with the systems. Our 3-series was RWD and that certainly used a combination of throttle and braking on the spinning wheel. Didn't stop it swapping ends in icy weather though. Winter tyres were a must on that car as being an MSport trim it had very wide rear tyres.

you will also notice some models have the option to turn traction control off or 2 options of off and sport.

Non technical explanations should be found from the links on this page http://products.bosch-mobility-solutions.com/en/de/homepage/homepage_1.html

As far as I know the diff is a standard open differential and it is made behave as it it is a torsen/limited slip by the ABS system braking the spinning wheel. This is more wasteful than a proper limit slip diff, but all the hardware is already in the ABS module, so it's a lot cheaper. This system is also used as torque vectoring, where the brake on the inside wheel is dragged slightly on bends to make the car pull into the bend better - I turned this on on my Superb II a while ago and it does make a subtle improvement when it's pushed into bends. Traction control still cuts power from the engine if both wheels are spinning though it's not as sudden and complete in cutting power as the previous systems. Haldex 4x4 systems connect drive to the rear wheels to see if there's grip there before cutting power from the engine when the front wheels spin.