Anyone had a P0420 code??

Hi all,

I have a 2000 Sentra GXE, creeping up on 100K miles. For the last few months the check engine light has been coming on and off, had it checked and it was the P0171 code. I finally took it to a shop about a month ago and they recommended that I replace the MAF sensor, which I did (very expensive!!). The car runs much better now - it was hesitating a little bit before and also stalled one time when pulling into a parking lot.

Last week the check engine light came on again, took it to Autozone and they read a P0420 code - Catalyst System Efficiency Below Threshold. I did some checking around online and the recommendations were everything from replace the catalytic converter, replace the oxygen sensors, try higher octane gas, etc. The car is running fine, just wondering if anyone has experienced this code and what they did to fix it.

Thanks.

Hi all,

I have a 2000 Sentra GXE, creeping up on 100K miles. For the last few months the check engine light has been coming on and off, had it checked and it was the P0171 code. I finally took it to a shop about a month ago and they recommended that I replace the MAF sensor, which I did (very expensive!!). The car runs much better now - it was hesitating a little bit before and also stalled one time when pulling into a parking lot.

Last week the check engine light came on again, took it to Autozone and they read a P0420 code - Catalyst System Efficiency Below Threshold. I did some checking around online and the recommendations were everything from replace the catalytic converter, replace the oxygen sensors, try higher octane gas, etc. The car is running fine, just wondering if anyone has experienced this code and what they did to fix it.

Thanks.

It is probably the cat, smell the exhaust and if it smells a bit like rotten eggs, replace it. 100,000 miles sounds about right for it to go out, and it shouldn't be much more than 70-90 bucks for parts and labor if you take it to a shop, or you could buy one from autozone and do it yourself.

I would have the catalytic converter inspected. If you Graph the O2 sensors and know how to read it, You would be able to see if the Catt is functioning properly or not by the activity of the rear O2 sensor. Also you want to see what your Alfa is , It should be around 100 % ( air fuel mixture ) It is also possible that the before replacing the MAF you could have been running rich dumping excessive fuel into the catt burning it up . i would check your catt converter function first

honestly, i had the same thing come up. the light was on for about 2k miles. all i did was change the oil, oil filter, and air filter, and it went away. hasn't come on since, so try that first, and start the car for 5 min, shut off, and do that a couple times, or make short trips. otherwise, u'll have to replace it.

It is probably the cat, smell the exhaust and if it smells a bit like rotten eggs, replace it. 100,000 miles sounds about right for it to go out, and it shouldn't be much more than 70-90 bucks for parts and labor if you take it to a shop, or you could buy one from autozone and do it yourself.

if the sensors are fine, then I'm sure it's the pre-cat,
cause there ain't no sensors after the 2nd cat.
and it's gonna cost u $500 just for the parts.

if the sensors are fine, then I'm sure it's the pre-cat,
cause there ain't no sensors after the 2nd cat.
and it's gonna cost u $500 just for the parts.

clean your EGR valve thats what i tell everyone at work, autozone. it'll save you money and clean your exhaust gases and keep it from setting off your check eng. light again.

Had a P0420 code right before the precat came apart and ruined my engine....Guess WHAT.... nissan would not fix it!

im glad you know how to use the search button.
welcome to af.

by the way, we ususally dont resurect threads older than 2 months tops in this secion of af.