Q: Q: Code p0421

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I am getting a p0421 code but I just replaced the catalytic converter. I got the code erased after but it popped back on. My car seems to stumble/put a lot though. What else could it be?

My car has 148000 miles.
My car has an automatic transmission.

Most mechanics will use a diagnostic scan tool to download the source of the error codes. In the case of the P-0421, we usually find that either the catalytic converter has run its course, or the O2 sensors are giving faulty data and need to be replaced at the same time. If you’d like, a certified YourMechanic technician can come to your location to help you diagnose this code or replace the O2 sensors in your vehicle. To be safe, we recommend replacing all of the O2 sensors.

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