I own a 1998 Mazda MVP with 126,550 miles on it. The check engine light comes on for a day or two then it is no longer on for a while and will come on again. It's been doing this for a few months. I own a diagnostic code reader which has read PO 420 catalyst system efficiency below threshold (bank 1). I've noticed a smell of hot metal when I stop driving. I've read several of the posts concerning the check engine light on and the PO420 code. What is the most likely repair procedure required. It sounds like the O2 sensor should be checked/replaced and then possibly it may require replacement of the catalytic converter. I'm interested to hear what your diagnosis is based on the symptoms.
Well if you are able to or know how. You need to monitor both front and rear 02 sensors for the front cat. 02s11 and 02s12 on your scanner (if you have one). If both 02 sensors are fluctuating (when the engine if hot) at the same rate. You more than likely have a bad cat. If one 02 sensor (02s11) is fluctuating but the rear (02s12) is steady, than your cat is probably ok and will require some more diagnosis.