i have a 2001 monte carlo LS and i bought it second hand, bad idea, the problem i have right now is my engine light comes on... i read the code 0420 on my obd2 reader and my dealer checked it and said it's because of my aftermarker catalytic converter... would an aftermarket catalytic converter cause this problem?

 

...yes

 

I get the same thing. I have heard from alot of guys that the best thing to do is change the O2 sensor, and that will normally fix it, for good.

Honestly though, in my situation, getting a code isn't a big deal, cause the performance that the cat helps with is worth getting the code that can be easily cleared. =)

 

the reason the 420 code sets is that it sees a rich/lean switching on the post cat o2 similar to that of the pre cat o2. the desired reading from the post cat would be a more even reading, the code is set by sensor activity rather than a lack of activity. p0420 wouldnt set if the post cat o2 is at fault.

 

so what could i do to fix this problem? replace the cat with a factory spec one?

 

O2 emulator will take care of it. After market CAT's flow outside the range of the stock O2 sensors. I have one on my car and have passed all emissions test so far.. Try ZZP, if they don't have it listed for the LS give them a call.

 

ok, i checked the zzp website and if i'm correct, the O2 emulator for their Grand AM is the same for my Monte Carlo LS... correct?

 

http://www.3800performance.com/Merch...oduct_Count=14

Check here, Rob is a good guy...

 

I would call before you place an order whether it be from 3800 performance or ZZP. I've ordered stuff from both and they are both up to speed on aftermarket stuff for your 3.4L. If memory serves me the 3.4L requires a different emulator than the 3.8L.

 

so if i replace the post cat sensor with the o2 emulator my car should receive better gas mileage correct? it doesn't give the ecm a bad o2 reading which would normally make it adjust the fuel/air ratio...