P0420 Code Cause/Diagnosis
I have a 2004 Lincoln Town Car. It's got a P0420 error code, with no other
codes. I have noticed slightly worse fuel economy, and it seems to
accelerate slowly at highway speeds. There's no exhaust leak as far as I can
tell. My question is, is it possible that the problem is just an O2 monitor, even
though there's no O2 monitor code? If so, how could I check for that? If it is
the cat, is it worth trying a cat cleaner?
With the poor acceleration you describe it's most likely a clogged catalytic converter. Your mechanic can do a back pressure test of the exhaust system to confirm this. I would suggest checking the engine and make sure it's running correctly. Not too lean or too rich, isn't burning oil, or leaking coolant internally. Unless you have a lot of miles on the vehicle, catalytic converters usually don't just fail. There's usually something else going on with the engine that causes the catalytic converter to fail! Hope that helps! Jim