How can i find out if it is working or needs replaced ?

Cheers James

assuming it's a vac one test for holding a vac --if there's no sign of oil leaking from the front/rear breather hole it should be OK but depending on use/milage might stand a good clean out

vacuum going into the saucer on top control the anti-shudder valve. You can manipulate that from the outside I think. There is another pipe going to the EGR itself, more behind it. As above, take vac line off the N75 box and try and get pressure down it to make it move.

the "flying saucer" is the egr -- asv is on the side and can be manually moved-- if you decide to remove and clean CUT the hose to the asv and refit later or the plastic nipple is likely to break off p.s it's vac not pressure! must be all that Devon air :-) d'rectly

Will it show up on a vagcom ?

Cheers James