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2018 equinox 1.6 diesel fwd. 73000 miles. Did oil change the other day and drove it 10 miles came home no leaks -level good closed it up. Wife went to work 2 days later and got a half a mile down the road and the check engine light came on. She came back home and took the spare car to work. I had the code pulled and it is p-0421 warm up catalyst efficiency . Vehicle has been trouble free since new and fluids and filters have been replaced regularly. i searched and only came up with 1 or 2 threads that have had this code.One went away on its own with no action from the owner i believe. I spoke to mechanic i know and he said this code can be a pain to diagnose. He suggested using seafoam in the tank of new fuel and that a lot of times a bad tank of fuel can cause this to happen .He suggested clearing the code a few times and hopefully it would go away. I am just looking for anyone who might have had this code come up and how they fixed it. I know if i go to dealer they will do the 2 recalls that are computer related and clear the code and send me on my way .
 

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Quote: I know if i go to dealer they will do the 2 recalls that are computer related and clear the code and send me on my way .


You may have answered your query.

Start there. Then Seafoam ( which never hurts anytime )
 

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Used 1 big bottle of sea foam in one tank full of fresh fuel.Got new code reader from amazon a few days later and cleared the code. Driven 250 plus miles and the check engine light has not returned and the code has stayed clear. I will update the thread if the code comes back again.
 

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If the code returns, could be a bad downstream O2 sensor. If your OBD reader can log data, it would be interesting to see what the O2 sensors are putting out. Maybe the downstream is changing too quickly - which could indicate a problem with the converter ... but not at that low mileage, I would hope!

Have you been driving a lot of short hops? If so, maybe a good hour drive at highway speed would be something to try...
 

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Says to follow Bulletin No.: 19-NA-009. Do you have a copy of that? I don't see it available online without a subscription ... but it probably just says "get your software updated"
No, I don’t have a copy of 19-NA-009 and was unable to locate it.
 

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I'd read up on the emissions warranty if it comes back again. I'm thinking that part of the warranty is for a pretty long time, and those parts could get expensive if you just kick that can down the road for now.
 
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