Just so you guys all know running the car with a bad head gasket, (like I did) causes anti freeze to be burnt, and thus ruins the cats. I am having this same CEL issue right now. 2004 model Changed the wires and plugs, seeing as they had 225,000 miles on the originals. Cleared the code. It came back after about 15 days of driving. LOL got my money out of those plugs. Today I'll change out the Rear sensor and clear the code again. We'll see if it comes back. In that case, I'll have to buy the cats I guess. Damned expensive from Subaru. And they will not ship me the perfectly good ones online, to commifornia. My plan is to have them shipped to my buddys place in Oregon, then he'll ship them down to me. They meet all the standards for California so I don't get why I cannot buy them here. Maybe someone can explain that to me.