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2001 BMW 325i: error codes P0420 AND P0430..catalyst..codes come

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I have a 2001 BMW 325i with 122000 miles. I have been getting error codes P0420 AND P0430 (catalyst efficiency below threshold on both banks). I've reset the codes twice and the codes come back in about 2-3 weeks. During this time, the car passed smog inspection with no problem. If one code or the other came on, I would assume the problem was an 02 sensor or a catalytic converter, but for both codes to come on simultaneously just doesn't make sense to me. One possibly related issue is that the fuel pump failed while traveling 75 MPH a few months before the problem started.
My question is: Is there any likely cause for for both codes to come on at the same time?

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Can I have the last 7 digits of your vin?

Customer: replied 5 years ago.
FU91792

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Before reading my answer below, please note that you must press the green ACCEPT button in order for me to receive credit for my time and effort. Thank you.

 

 

 

 

 

 

 

 

 

 

These codes are generally caused by a bad cat, or possibly bad o2s. Also a clog could do it as well.

 

However, they can also be caused by an exhaust leak if you are looking for a possibility for both at once.

 

I would check for an exhaust leak. If none is found, a proper real time diagnostic on a sophisticated diagnostic computer that can read live data would be advised, as trying to solve this using simple p codes will be very difficult.

 

I hope that is helpful, please let me know if you have further questions, or if I can clarify anything for you.


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Steve

 

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