So my car has been sputtering only at 60 mph. Just recently I was able to obtain a scanner and the scanner read P0420, Catalyst System Efficiency Below Threshold (Bank 1). But today while driving, the sputtering went away at 60mph and doesnt sputter anymore. but the CEL is still on. Is it the Catalyc converter or sensors?
it is really hard to say what you may need to do is get a shop to run a better computer on it or take it to a muffler shop and have them test the cat with a infared thermoter to see if its a simple pluged cat or if you have a faulty O2 sensor what kind of motor do you have will help out call your local parts house and get a price on new O2 sensors if you have 80,000 or more miles on your car after doing some research im almost certain you are having O2 sensor problems you might also change fuel filter and run a Seafoam 8-10 dollars a bottle you really should try this now mind you it will cost a little bit for the O2 sensors but keep in mind if they are bad your gas mileage will drop drasticly because your O2 sensors regulate the fuel and air mixture and keep the car from running to lean or to rich optimizing your gas mileage and the performance
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