I have a 2003 325i with the referenced light on. I have done some research and it seems the most likely culprit is the gas cap. I have removed the cap, cleaned the inside and re-installed it. No change, light still on. . It clicks when I tighten it. It appears that the O ring has cracks in it and might not be sealing correctly. My question is, should I replace the O ring or the entire cap or is there something else I should check before doing that? When checking the codes with my OBD Fusion, I get a PO456, which is apparently the code for the above problem. I also get pending codes PO175 and PO172 system too rich. I don't know what that means so any information is appreciated. TIA.
Service engine soon light
