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Q: The engine light is on and the code is P0420 - Catalyst System Efficiency Below Threshold Bank . What part do I need to fix it?

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The engine light is on and we just want to know what the part needed to fix this issue. the code is P0420 - Catalyst System Efficiency Below Threshold Bank . However I dont know if its downstream or upstream.

My car has 130267 miles.
My car has an automatic transmission.

A: While a number of things like a faulty oxyg...

While a number of things like a faulty oxygen sensor or exhaust leak can cause fault code P0420 to be set, the most common fault is the catalytic converter itself. However, as a replacement can be very expensive, your best be is to have a certified technician properly diagnose why code P0420 was set in the system.

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