ACF Connecting Pipe?

[ub7rm]

I had an email from the dealer to say that there are three outstanding campaigns on the car,

One to correct the service interval...
One to replace trim at the rear window.
and One to replace the ACF connecting pipe if required.

What is the ACF connecting pipe?

 

[ub7rm]

Found out its the activated charcoal filter, apparently some are failing prematurely and are being routinely checked.