I have been battling my Check Engine Light for a while now. I had been getting 2 codes: P0421 and P0340. I cured the 0340 by replacing the Cam Position Sensor. As far as the 0421, I have done plugs, wires, and coils, and the light keeps coming back on. So, I desperation, I took it to the local parts store to have them scan it, and 0421 came up again. Their readout says that it could be a bad cat, ignition system issue, or a rich air to fuel ratio. Not sure how it could be an ignition issue, as I replaced those parts. So, in your experiences with the 2004 Sante Fe with the 2.4, what would be the most common / logical route?