dannieboiz

On my W211, when I go downhill it shifts to a lower gear to slow the car down. On the same hill that I go on daily the s doesn't do it.

Diesel Benz

Never heard of downhill assist but your W211 has SBC brakes but it does not use those to keep the speed steady at downhill while your W221 does (the facelift W211 does also, even if it does not have SBC brakes any more).

Actually I have so few places to observe the difference, I thought the W221 would use engine braking in addition to brakes but likely not too aggressively. The W211 might use more engine braking when it does not use brakes.

I guess your speed stays steady anyway with the 221 also at downhill parts of the road?

Honestly I tend to switch CC off when the car starts to brake, in my case the car would not gain speed more than 5 mph anyway and I hate brakes being used to kill the speed (means additional fuel consumption and brake wear, even if only marginal).