P0455 code along with strong gas smell

I have a 2001 X5 3.0........I recently had the SES light come on and checked with a Autel code reader and got the P0455 code. I can smell gas pretty strongly from time to time near the rear passenger wheel well. I would like to know if this is a vapor solenoid issue or the charcoal canister giving me the code? I also need to know the location of both of those items?I checked the obvious gas cap and it seems to be ok.....Oh if you have a diagram or picture that would rock!