I am getting a p0420 code. i have an aftermarket evan fischer cat about a year old. I have tried to use non foulers. I tried 4 short non foulers. 3 non drilled and 1 drilled and still got the p0420 code. Would this ecu throw this code if bursts of air such as the cat being clogged because the air is not constant. does the non fouler trick work on a 2004 a4 AMB engine? 151000. No other codes at all.

 

The code is set when the output of the downstream sensor follows too closely the output of the upstream sensor. This happens when the exhaust coming out of the cat is basically the same as when it went into the cat. I suspect that either your cat is not up to the task, or that the downstream sensor is installed in a bad spot. You could try looking for O2 simulators to be used in place of the downstream O2, They are avilable for many cars, but I a not sure about yours.

 

I understand the concept of the post cat 02 sensor and what it does to great detail along with the pre cat 02 sensor. But four non foulers should set the air way different ten what is read by the pre 02 sensor

 

its not the sensor. ITs the cat itself. There is a different code for the o2 sensors. Cant think of it off the top of my head.

 

figured it out

 

so what was the verdict so others can know too.

 

the verdict is that it is essential to drill out the non fouler with a 1/2 inch drill bit otherwise the holes on the oxygen sensor will not receive any 02 at all making the computer throw a code. my setup is 02/drilled short fouler/short non drilled fouler/ cat. im sure it would work with just the short drilled fouler because my cat still works but just wasn't efficient enough and didn't clean the air as well as the AUDI one. haha tree huggers. so moral of the story make sure you drill the non fouler directly by connected to the 02 sensor.

 

cel came back on after 1200 miles of driving any ideas? ive already had the ecu reflashed. and there are no holes in the exhaust and maf has been replaced and so has post cat and pre cat 02 sensor

 

im telling u i believe its the cat. there are different codes for the sensors and the cat. Ive had that code on my car for over a year. I just clear it when i get bored and it always comes back. Even with the sparkplug fouler it wont get rid of it. Only way is to get a new cat or get a tp or get a hfc. Tp being cheapest hfc being cheaper and new oem cat making you go broke!~

 

I agree ^ ..... almost 98% of the time, the P0420/P0430 codes indicate a bad converter. Rarely will anything else including o2 sensors, cause this issue or DTC