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Need some input here: CEL came on yesterday after a 350 mile journey. It was running the COBB stage 1 tune (the only modification I have on is the complete mountune cold air intake kit). Checked out the error code on the accessport and got the P0420 error code (catalyst system below efficiency threshold, bank 1). Reflashed the car to stock tune in prep to taking to the dealer and now the CEL is gone. The flash port isn't detecting any error code. Drove it on the stock tune for a bit...CEL didn't come back on...reflashed it to the mountune tune and drove it more...yet no CEL..car seems to running fine...appropriate boost n all...not sure what to make of it?
 

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Search is your friend. Here's the first result on duckduckgo for "Focus rs P0420"


When did you get your HG done?
 

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Need some input here: CEL came on yesterday after a 350 mile journey. It was running the COBB stage 1 tune (the only modification I have on is the complete mountune cold air intake kit). Checked out the error code on the accessport and got the P0420 error code (catalyst system below efficiency threshold, bank 1). Reflashed the car to stock tune in prep to taking to the dealer and now the CEL is gone. The flash port isn't detecting any error code. Drove it on the stock tune for a bit...CEL didn't come back on...reflashed it to the mountune tune and drove it more...yet no CEL..car seems to running fine...appropriate boost n all...not sure what to make of it?
Sounds like the cat isn't getting to operating temperature or one of the sensors has drifted out of range. Could be a hiccup.

Ciao
 

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Search is your friend. Here's the first result on duckduckgo for "Focus rs P0420"


When did you get your HG done?
I bought mine as a CPO, so the HG was already done.
 

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quick note here.

2017 RS, 14K miles, threw the p0420 a week or so ago.

I took it in, and they are replacing the cat under warranty.
I'll say this as well: This is about a month after I had my head replaced (was cracked, also replaced under warranty).
I wonder if residual accumulation of stuff with a cracked head built up in the cat, and caused this failure.

We shall see.
 

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quick note here.

2017 RS, 14K miles, threw the p0420 a week or so ago.

I took it in, and they are replacing the cat under warranty.
I'll say this as well: This is about a month after I had my head replaced (was cracked, also replaced under warranty).
I wonder if residual accumulation of stuff with a cracked head built up in the cat, and caused this failure.

We shall see.
Was the head leaking coolant into the combustion chamber? If so, that's a good way to kill a cat
 

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There are lots of threads about this code. I just posted in this one over here:

I think there must be something inherent about the car that fries cats (pops n burbles?) because I have now gone through 2 cats in less than 30k miles. Totally stock car, no symptoms, head replaced at about 12k miles before the first cat went out. Coolant levels are fine.

I’m asking the dealer to do a thorough check but not expecting him to find much since there are so many others who have had no symptoms and popped this code. Maybe the sensors just tend to read wrong under certain conditions?
 

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I have received the same CEL since I installed a new catted downpipe. It comes on randomly. Sometimes when driving, some times at startup, sometimes when at higher RPM's.
I expect it is the aftermarket downpipe causing this. I also had this issue when I had the stock downpipe on too. In my case, it is tuned, custom intake, K&N air cleaner, and other mods.
 

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Purely informational dtc, no issues related.

These cars are very hard on cats.
 

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My old ‘12 Focus Titanium threw that code around 50k-something, and it was indeed the cat.. on a Ti no less! So uh, you’re not alone?

Had it replaced under warranty.. Course then the DCT blew less than 10k later.. had that replaced under warranty, put an order in for a RS, sold the Ti privately, & picked up my RS.
 
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