Q: Code P0420. Need to replace catalytic converter.

Hi there. The code P0420 is coming up for the Downstream Oxygen sensor has picked up an abnormal reading and is saying that the catalytic converter is below threshold. There could be a misfire on the engine, leaking injector, ignition timing retard, engine coolant temperature sensor not working, a leak in the exhaust system, a faulty Oxygen Sensor, or a faulty catalytic converter. Before replacing the catalytic converter, I recommend checking all of the above information and see if your engine is having an issue. If there is no misfire, the injectors are replaced or cleaned, the ignition is normal, the coolant temperature sensor is working, there is no leaks in the exhaust system, and the Oxygen sensors check out to be good, then I recommend replacing the catalytic converter. 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.