Not sure if this is an issue or not but on my 2009 535i, the front parking sensors do not switch on unless 1) the car was previously put into reverse, 2) they are manually switched on. It becomes an issue when you drive the car towards any object if parking etc. Even pulling the car into the garage they do not come on automatically
My other car (Non BMW) the front parking sensors come on automatically when the car drops below 20 mph.

Is this std on these cars?

 

What you describe works the same as mine. Push the button or auto when goes into reverse.

 

is there anyway it can be activated? when i drive the s class around i get used to it esp when in tight traffic, on the e60 it has to be pressed manually

 

This is "normal" operation for cars equipped with PDC. So, if you're pulling into a space (PDC won't activate automatically unless you first put the car in REVERSE) or by pushing the button when driving forward.

If that is awkward or inconvenient (I do) you can use voice activation of PDC by pushing the "talk" button on the steering wheel and saying "PDC"!

 

Thanks everyone. I'll try the voice activation just for kicks as it's easier to push the actual button itself

 

Yes, particular feature of MB. Nice feature, too, although the warnings in the E60, with the graphic automatically taking over the idrive screen and the loud beeping, etc., would undoubtedly drive anyone who drove in city traffic absolutely insane.

 

Yeah who would want that beeping going on for every little thing, especially in traffic! And do you really need a warning to see WHAT'S IN FRONT OF YOU!