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Mike V.
Mike V., Technician
Category: Kia
Satisfied Customers: 25312
Experience:  I have 25 years experience working on cars. I am also a factory trained Subaru and Nissan Tech.
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Emission Failed code p0421 warn..below one..downstream

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Emission Failed code P0421 warn up Cat Eff below threshold bank 1...what's wrong which side is bank one I replaced the downstream sensor driver already
Hi Sir or Madam Thank you for choosing JA, I will do my very best to assist you with your concern.
Hi there!
This code is for the first converter on bank 1. This is the converter right at the exhaust manifold. Since the sensor didn't resolve the code, most likely the converter will need to be replaced.Basically, the converter isn't storing enough O2 to clean the exhaust.

Hope this helps!
Customer: replied 5 years ago.
I changed the 02 sensor on the driver side not the passenger side should I first try changing the 02 sensor on the passenger side before venturing out to buy a new cat for the passengedr side. Which side is what Bank 1 passenger 2 driver side
The code is for bank1. Bank 1 is the passenger side of the engine, or the one without the oil fill hole in it.
It is possible that the sensor is the problem, but no way to tell without a scan tool that can read the live data. So, purchasing a sensor is really up to you. I have seen the converter as the problem, way more then the sensor.
Customer: replied 5 years ago.
I have 185,000 miles on the vehicle. With that in mind which one would you change. hate to buy a cat and it not work and how does a cat attached clamping or weld it in place
I suspect with that kind of mileage the converter will need to be replaced.
I believe it is a welded part of the exhaust manifold, if not, then it's bolted to the manifold.
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