P0420 Code Cause/Diagnosis

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

My 2004 Lincoln town car is doing the same thing. It almost kind of lopes at an idol and occasionally I will die if you let it idle and drive with a break on for too long. What do you step on the gas it’s stutters and stumbles do you get the RPMs up a little bit and then it just moves right out. I was told it could be a vacuum leak somewhere causing all that. I’m getting both codes for a lean burn situation on bank one and bank two. I’ve heard this can be from a vacuum leak to just simply a bad O2 sensor or two. Just seems crazy they were both go at the same time but in the same day. It’s got 287,000 miles on it original engine exhaust etc. Maybe it’s time for something to go then? I live in an area where smog is not mandatory so I was thinking about getting a remodel bit like a Flexi bit and hogging out the cats suck and all the debris out with Shopvac and see how it changes. Also should probably get new O2 sensors. Only after a test each individual one out of the four upstream and downstream. Then the stuff I said sound famiar to you guys? Thx.