Charcoal filter absorbs fuel odors when you fill your tank. They do need to be replaced occasionally. I understand that if you frequently top off your fuel tank after the fuel nozzle has clicked off that you can shorten the filter life. Get the Haynes manual for the V70 (available from IPD or Haynes UK) ISBN 1 85960 573 7. Page 4B-5 shows pictures of the canister and says that it is located under the left-hand wheel arch at the front. Also check Bay 13. Doesn't look that difficult to replace but the canister has a vacuum valve on it and the valve and canister are built together so maybe the part is expensive.