Advice needed for my 1 series

[Ajw]

Hi I’m looking for some help/advice on my 1 series, it’s 2013 116D . Last few weeks and only when it’s raining and doing over say 50mph the car suddenly tries to stop. It happens quite  rapidly and the speed decreases by around 10 mph before it will let accelerate back to the original speed. I’m not sure if this part is related but I can also feel the hill assist trying to kick in when on a flat surface not a lot but enough to notice/feel it. I’ve had my local garage check it over but they couldn’t find a solution and I was also told that the cars are fitted with some kind brake self cleaning software that tries to keep the pads clean in wet conditions. I was also told that grommets in the brake fluid reservoir had a recall and that a quick way to check if that was the problem was to change the brake fluid out, as the fluid might have turned bad with condensation but all was good there. Sorry for the long post but wanted to give as much info as possible. 
 

if anyone can advise or has come across this pls could you let me know what it could be. 
 

many thanks in advance 

[Greydog]

Morning Wayne

Welcome to the Forum

You need a diagnostic scan by someone with a BMW capable system 

Dave