I have a check engine light on caused by a 0455 fault code. I checked the all the hoses and canisters. Everything looks good. Should I replace the canister close valve or purge valve? Car runs great, no gas smell or noise.

 

Is it an OEM gas cap? If not, definitely replace. Check the sealing surface where the cap meets the filler neck. It must be a uniform fit or it will leak vapors. I'm pretty sure there's a TSB for an 01 and older XK. I may be wrong though. I'm just going by memory. Check for TSB's here in the X100 section to verify.