Car is fit with a Max Speed aftermarket exhaust system. Twelve hundred miles on these and I get the check engine light in my face. Code P0420..
cat system efficiency below threshold bank one. cats on these look like a box full of small straws. Do these fail/ plug up or am I looking at replacing the downstream O2 sensors? Have already replaced the primary sensors. Any input would be greatly appreciated.

 

It's likely the cats. You can reset and see if it doesn't come back. Don't throw parts at it quite yet. Feel free to can I would be glad to help.

 

Can they be cleaned if they are actually the problem?

 

Clear the codes and let the cats get good and hot before you drive, see if it comes back.

 

any pending fault codes? ...like a p0430..?

 

0420/0320 are due to the rear o2s seeing too much. Those cats aren't working too well. Add some extenders and reset the codes and you should be good. Either way, the codes don't hurt the car.

 

Will give this a try...thanks

 

Only code to show up is P0420

 

Extenders Going to try clearing codes, heating the cats then off for a drive. Am aware that codes will not harm the car but the dash warning light drives me nuts....electrical tape will fix that

 

Also try to keep your rpm over 3k when cruising. This is good for the bearing oil system also.

 

 

It's not that they are dirty it's just the quality and their ability to remove excess fuel in the exhaust gases coming out from the engine. Spacers are a good idea because they will compensate for this quality

 

I bet they will work if run efficiently. Good temperature and not lugging the motor.

 

I throw this code all the time (i don't have cats). I just clear it and it comes back every 150 miles or so.

I've been told I just need O2 simulators or extenders or something but no one can ever tell me what exactly to buy to fix it so I keep a OBD reader in the car and keep clearing codes.

IIRC the code does impact the fuel trims so it's best to reset the codes when they appear?

 

Worth a try...where does one purchase these spacers or at least get a drawing so I can make them up?