Q: Repeated Cat Code: P0420 keeps coming up.

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I bought this small pickup after a friend of mine passed away from a heart attack. 1999 Dodge Dakota Sport 4x4 with 82,500 miles. I got it for cheap, replaced the transmission, tires, etc. to get it up and running. About a year after having small problems, a larger problem popped up. Check Engine Code: P0420. Took it to Firestone and had the Catalytic Converter replaced for a not so fun charge. 3 months later, the same code comes up. Took it back to Firestone, and they replaced the O2 Sensors. Again, around 3-4 months later, the same code arises. They replace the Catalytic Converter again free of charge because it is under warranty. 3 months. Same code. Took it to Firestone, and they refunded my money and told me to go to Dodge themselves. Dodge tells me 97% sure, they need to replace the O2 sensors for $600. Okay. Done. 50 miles later....same code. How do I get rid of this??

My car has 82500 miles.
My car has an automatic transmission.

Hi there. The code is coming up for more than the O2 sensors or Catalytic Converter. Perform the following steps to determine what is the cause for the code P0420.

Check the following

  • A damaged or failed oxygen sensor
  • The oxygen sensor wiring damaged or connected improperly
  • The engine coolant temperature sensor is not working properly
  • A leaking exhaust manifold or a leak in the exhaust system
  • The spark timing is retarded
  • There is a leaking fuel injector or there is high fuel pressure
  • The engine has a cylinder misfire
  • The engine oil is contaminated

If you need further assistance with your check engine light being on, then seek out a professional, such as one from Your Mechanic, to help you.

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