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Code 0420

Got a 1997 Mitsubishi Mirage with this code. Only had car a while. It has always had a hesitation accompanied by the CEL coming on and then going out. Might happen twice a trip and then not occur for weeks. Previous owner said they failed an emissions because he cleared a set code(not told to me). The car dives fine and gas mileage seems to be fine. Car does use about a quart of oil over a 3000 mile oil change. It also has/had a rattle similar to an exhaust baffle…the rattle is not an every trip occurrence either. Had Autozone check for code and was told catalytic converter needed to be replaced. There are no emissions in my state but I would like to know any opinions on my problem and any issues with driving car without repair. I think I want to clear code by disconnecting battery cable and see if it returns but not that would be a good idea. Also considered buying a scan tool with live data to see if there is another issue that might not involve replacing the catalytic converter. looks that option could be expensive too. Thanks for any and all help and comments. Previous owner also mentioned a hissing when removing gas cap and he bought another cap but the I still notice the hissing.

The P0420 code has been discussed ad nauseum, please use the search box for “P0420” lots will come up. It doesn’t necessarily mean you need a new converter.

This is why I don’t like the free code reads that chain stores offer. They are not free they are a sales tool so you buy parts from and hopefully fix the the problem. P0420 is catalyst below efficency, yes cats can cause this code but bad a/f sensors, exhaust leaks and ecm issues can also set this code. Spending some money to have a good shop perform a diagnosis would be a good idea.

If your car has been sneaking and around smoking marijuana it can cause this code to pop up.


Perhaps the cat really is a goner. What if that rattling is the monolith broken around, rattling, causing a restriction?

In any case, a proper diagnosis is money well spent