Q: I have a po420 code and suspect my flex pipe between the two cats is leaking. Could that be a possibility of why that code is comi

asked by on July 25, 2017

I'm getting a po420 code. I am experiencing slow acceleration. My exhaust setup is cat attached to manifold into flex pipe into a second cat with the only 02 sensors before and after the first cat. Is it possible the code could be from a small leak in the flex pipe? If not what are the chances it's the second cat even though there's no sensors after it??

The downstream oxygen sensor (post converter) monitors the efficiency of the catalytic converter. If there is no downstream sensor after the second converter then the P0420 code cannot arise from a fault there. Exhaust leaks have to repaired anyway, due to the risks of carbon monoxide poisoning, so the best thing to do is repair the leak. Although in certain circumstances leaks can cause P0420 to set I wouldn’t count on a resolution but, as noted, the leak has to be repaired anyway so that is a good place to start. Generally, P0420 sets due to catalyst efficiency being out of range but there are many engine operating problems that can cause out of range catalyst operation. In other words, P0420 does not necessarily mean the catalyst itself is performing poorly; it could be an engine issue. Although, in your circumstance, with slow acceleration, and a P0420 code, a partially blocked converter would be considered in the diagnostic. The bottom line is, to resolve your issue the recommended service is a slow acceleration diagnostic. If you request that service, the responding certified mechanic will get this taken care of for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.

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