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Hey everybody, I'm getting an intermittent o2 code p0420 below factory threshold. Afe headers, kooks green cats and Awe track exhaust. I want to say i can make the light come on while running in manual mode and in 6th gear low rpm's kinda cruising along. but haven't really tried on purpose, just seems coincidental that's when it happens. seems when i run the same way in 5th i have no issues. someone said get o2 sensor extensions. I've checked all the bolts and gaskets for leakes and were good there. i'll swap the o2's this weekend and see if the code follows. thx
This code occurs because the aftermarket cats don't work as well as the oem version. I had this issue on my own car after headers/high flow cats and it took me a while to solve it but I did with an interesting product. O2 sensor extensions did not work for me. What I found that did work are these mini cat o2 extensions. Big daddy mini cat cel fix I know the name is kind of funny and the website is cheap but these thing worked perfect. They are also a little pricey so I was tempted to get the eBay knock offs but don't. Just get the real part and be done with your problem imho. Once installed you have to do a full drive cycle before the code will clear out of the system. If you have put on several hundred miles since the code set it will become permanent and stored in memory even if you clear the code with a handheld scanner. Only a full drive cycle will remove it from memory if that happens. I forgot the drive cycle procedure but I remember it was kind of a pain. I'll post it up if I can find it in my history on camaro6.
hope this helps
Last edited by jimmypop13; Nov 15, 2020 at 01:41 PM.
To do a drive cycle for the o2 sensors to clear their codes or permanent codes if set, this is the procedure:
"GM uses a two-part HEGO monitor. The first part of the HEGO monitor runs after idling the engine for two and a half minutes with the A/C and rear defroster on. This checks the O2 heater circuit. After this, turn the A/C and defroster off, then accelerate at half throttle to 55 mph and hold at a steady 55 mph for three minutes. This will complete the second half of the HEGO monitor that checks the responsiveness of the O2 sensors."
The first part was easy. The second part of driving half throttle to a steady 55mph for 3 minutes was the hard part. Even on mostly empty roads I'd always find some idiot that ruined it. I'm not sure why it's 55pmh and not 65 or 70mph because then everyone's pissed off at you on the highway too. It took me several tried but I eventually got it done and the permanent codes I set cleared
Last edited by jimmypop13; Nov 15, 2020 at 02:02 PM.
I didn't get a chance to swap the o2, had to go out of town for the weekend. I'll swap it today. This code is on a 2020 c8. i've always been able to clear the code within hrs after it comes on. sometimes it's a few weeks before it pops on again. I think swapping the sensor will tell me if it's bad or the actual p0420. Thanks for all the input so far. will keep ya posted. Man i love this car.
Talk about bringing back a thread from the dead. I’ve had my cats for few months and about two or three track weekends and now I have the P0420. Doesn’t surprise me being the car is pushed hard. Every car I’ve owned does this with cats or test pipes. So I’m going to buy the Big Daddy Mini Cats (O2 Extenders) from the link above. Might be a tight fit for the location but what isn’t on this car. Hope it’s a good call and that I don’t need the 90° ones. Might have to remove the little metal bowl/ heat shield around the O2 sensor. We’ll see.
Paragon cats if I recall correctly? Big Daddy makes quality spacers so I'm sure they'll work accordingly.
I have the AFE ones I got through Paragon. Believe it was the last set they ever made due to emission laws where they’re located. I’ll keep us informed when I get them. They seem to have great reviews across the board.
Last edited by NoMatter; Apr 20, 2022 at 08:20 PM.
Got the Big Daddy Garage mini cats in today. After 70 miles so far I’m running good. It was coming on after just 10 miles every time I reseted with scanner/ battery. I had a great faith in this product for ever car I’ve ever ran required this particular mod rather if it was just O2 extension or mini cats.
I do feel most all cats will be fine under normal conditions. IMO after several track weekends it wears and will expose these common issues.
Tempted to get a set of blankets for mine, but so far the ceramic coating seems to be working really well. We'll see come TX summer heat though; looking at doing a roadtrip down to Big Bend National Park so 120+F ambient temps aren't out of the question.
Getting a p0420 code
