Intermittent P0421/P0431 on 575m

Hi folks, I've been getting intermittent P0421/P0431 and I want to try and get to the bottom of it. I've been clearing it whenever it popped up and living with it since car is running just fine. So last month I had a slowdown light and my mechanic replaced the cat temp sensor controllers. We were surprised to see original controller with 2002 date codes. Plus my car had 61k miles now so they held up quite well. Anyhow, our plan is to replace the O2 sensors next if the check engine light pops up. I just want to check with you all to see if you folks had similar issue before and what the usual culprit is. Worst case, if the codes come back after chaining the O2 sensors, i'll probably change the CATs with high flow ones from larini or something. Any other possible causes?

P.S. one thing is, when the codes come on, both sides come on together. Is it likely that both sides crap out at the same time? Or one bank automatically triggers the other by design? Or they are independent and should come on separately. If they are independent, i'm thinking maybe something up stream like air injection pump or something crapping out during cold starts etc.

 

I'd be curious to know how the 757M measures cat efficiency. Front and rear O2 sensors seem to be in the header (manifold), not in front of the cat and behind the cat like the 550.

https://www.ricambiamerica.com/car-diagrams/ferrari/v12/gt-group-2-seat/575m/front-exhaust-system.html

With 61k miles, it probably is time for a cat change. Can you get a boroscope into the exhaust system to check back of the cats on a 575M?

 

Ian- The 575M (and 612 and 599) have four precats in the headers, unlike the 550. Ferrari needed to do that to pass emissions until the 599 GTO came out and improved technology allowed them to eliminate the precats and go to just two primary headers.

 

Thanks, Taz! That kind of complicates things. If the car is measuring the efficiency of pre-cats (and not the main cats), what could cause (pre-cat) inefficiency codes, but also cause main cat overheats (causing a slowdown light)? Of course, both pre-cats and main cats could be disintegrating.

Sounds expensive, whatever it is. Time to pull the exhaust system to pieces and do a full visual inspection?

 

Thanks for the replies gents. I'll try and talk to my mechanic as well and see if he can check things visually. I'm not sure how often the pre-cats fail. If main cats i think it's probably easier and cheaper to replace if I go aftermarket route. For pre-cats I am not sure what options i have. Especially in California... maybe time to register the car in Montana and go cat-less .. Thanks again gents!

 

I had an intermittent slow down lamp and power cut on my 575M and swapping out the two thermocouples cured the problem. No further problems and all my lambda (O2) sensors are originals.

 

Thanks for the info again Taz.. I will put the on the swap out list. What’s interesting is that when the check engine comes on it comes on for both banks at the same time. So maybe it’s more up stream? Anything that might trigger the codes on both sides at the same time?