Hopefully this isn't repetitive, I've had my car for two weeks now. It's a 2006. It has been running amazingly, then BOOM CEL comes on. I hook up a OBD II, and it says Lean System Bank 1. So some techs I know as well as myself, decide that it is the O2 sensor. I took it back to the dealer because they were going to fix it for free, they diagnose it as a mass air flow sensor, and replace that. Just as a small background, it has a nismo intake and a HKS exhaust cat back system on it (they are trying to say that may be the problem ). The guys at the dealer say that it is possible that the light will come on again, and that it may be because the car has a tune, although I dont know if that is the case. So I guess what I am asking is has anyone had this similar problem? Or are G35's prone to having bad O2 sensors? I apologize if this is in another thread. Thanks for your help.