I think the cats need to warm up to be fully affective. If the car was not driven a bit before the test or sat for a while before the test, it can fail with everything functioning perfectly. This happened to me before on a different car. If your numbers are close to passing this may be the problem. When it happened to me I just went back for the retest after driving it a while to heat up the cats, passed just fine. Hope this helps, if not sorry for the babble. MArk
