I failed my emissions test cause I have my service engine soon light on and it gave me a P0420 code. My car is fine though and I heard it's because of my upgraded headers, I guess the computer doesn't recognize it so the service engine soon will turn off and on. I told the emission guys that was the case but still failed. What code is a P0420? Might be O2 sensors. Anyone? ?

 

im an emissions inspector p0420 is catalyst system effiency it may be due to the 02 sensor headers burn up o2 sensors there is ways around that or your catalytic converter may be fried i would replace the two sensors and clear code what state are you in???? how many obd2 monitors do they allow to be unset

 

I'm not sure, but I'm in Chicago, Illinois. You think header gaskets have anything to do with it?

 

PO420...Catalyst System Efficiency Below Threshold, bank 1.
You have an oxygen sensor in front and behind the cat converter, among others. When the engine is warm and in closed loop mode, the front oxy sensor reading should fluctuate, and the rear oxy sensor should read more steady. If the two sensors have similar readings, it means the cat converter isn't working correctly, and it will trip an error code.
Did you gut the cat, remove the cat, or mess with the oxy sensors at all?

 

he has headers the headers will screw up the oxygen sensors i see it alllllllllllllllllll the time i actually just failed someone for the same thing haha

 

no the gasket wont affect it is the sensor you probably will need to replace both of them if that doesnt work your catalytic converter is junk you would need a new one

 

My catalytic converter is a magnaflow, had it on for about a year now and after that I had to replace the O2 sensors, but you know how machanics are. So it could be O2 or the converter. Actually when I put new O2 sensors last summer, he hold me he couldn't reach the third sensor cause it was pitched or something by the headers when I got them installed. Guess I'll find out when I have time to take it in. I have til the end of november.

 

Good luck

 

Yeah good luck. Some of those test guys can be real bassterds!

 

hey now we arent all bad haha in all honesty there is nothing we can do about obd2 cars if lights on computer fails it thats all there is to it really if we forewarn u that car will fail cause light is on we can lose our license