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Discussion Starter #1 (Edited)
Good day,
So my 2008 MDX at 150k miles just threw a P0420 "Catalytic Converter System, Bank 1 - Efficiency Below Threshold" code. It comes on and off on it's own and tends to be less prevalent when we see warmer days this winter season.
In looking to purchase and replace my catlaytic on RockAuto for parts, I have an option of "Front Left; Radiator Side" or "Rear" Catalytics. Any thoughts on how to deduce which one to replace? Thoughts?

Thanks,
 

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Bank one should be the radiator side or upstream but don't quote me. I dont even know how many cats are on this car? Is it two on both banks?
 

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You do mean P0420 rather than P0240, right?

P0420 is bank one or the firewall side of the engine. There are actually 3 converters on this car. One for each bank just off the manifold and a 3rd after the exhaust merges to one pipe. The 3rd one isn't monitored. This particular code relates to the downstream sensor on the exit side of the converter.

In most cases this code indicates a converter that is flowing just fine, but not cleaning up the exhaust to within the parameters set for the ECM. I performed the non-fouler hack on mine 5K miles ago and the CEL has stayed off. The car runs just fine. I don't live in a smog test state, so I have no idea if it would pass, but others have posted on other forums that their car still pass a smog test. The hack simply spaces the O2 sensor out of the exhaust stream a bit to make it less sensitive. There are videos on YouTube to show you how it's done and it literally costs about $10 to do it.
 
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