the 455 code is a large evap system leak. Often it is the fuel cap. On mine I replaced it and still got the occasional 455 code.

I don't know if this was the actual culprit or not, but the vacuum elbow off the manifold (inside of the power steering pump) and under the upper radiator hose had a hole in it. I guess this is a frequent failure. Hard to get at, but I was patient and was able to replace it. No more 455 code since then.

I have read that bad vacuum elbows can cause all sorts of wierd codes. There are only a few to worry about, so you might want to check them.