i have a CEL on and it gives the code PO420 which means... Catalyst System Low Efficiency. as it is stated in the CEL sticky on this page however idk what i need to do to correct this code. i tried to just clear it and see if the problem came back. it has been almost a month now and it just came back on. has anyone had a similiar problem or can just help steer me in the right direction as to how i should fix this problem??? i replaced both O2 sensors about three months ago. for my exhaust i have an aftermarket header, 2.5" pipe back to a 46" long resinator, cat converter, back to an aftermarket muffler. any imput would help. thanks in advance!!!

it's either a bad o2 sensor in the cat converter, or a bad cat.


Desert Tuners

“When you come across a big kettle of crazy, it’s best not to stir it.”

how do i know what it is? or how do i test either one???

kinda hit or miss really. see if someone you know has an o2 sensor. takes yours out, put that one in. get the code cleared and drive the car. if the code comes back after a day or two, it's the cat. if it doesn't come back, it's the sensor.


Desert Tuners

“When you come across a big kettle of crazy, it’s best not to stir it.”

the worst thing with that is that it went a couple weeks since it came on... but i guess i'll have to try something!

Well, I just replaced my cat a couple weeks ago for the same reason. You will know when the cat is bad, it will stink something aweful and the car won't run as good. Probly lose some MPG also.

Aaron


97 Cavalier Z24 @ 85k
00 Cavalier Base Coupe @ 152k...rollin on 14's!
97 Grand Cherokee 5.2L@ 260k

well i've never smelled anything! however now that you say that i was racing a friend of mine and ppl said that i was trowing out flames from my exhaust idk if this was from this problem or it was just because i had a carbon build up from making to many short trips... however i haven't noticed any drop in mpg i seem to always stay around 28-30...

Is this the only thing that this code could be?? because if it is i think i'm going to replace the O2 sensor (even though i just put it in like 3k miles ago) and see if the problem persists... b/c i don't ever smell n e thing from the exhaust...

GET A FREAKING SCAN TOOL, DOES THE REAR O2 SENSOR MIMIC THE FRONT 02 SENSOR, IF YES IT IS BAD, IF NO IT IS SOMETHING ELSE


- 2004 Cavalier - 124k, owned since new

ok... i'll try that tonight or tomorrow and see what happens... thanks

You need a scanning program like HPT, or something. See what the rear o2 sensor is doing. It will not always mimic the first sensor. Mine went bad it would go from like .000 to .5 nothing else or in between. You can also put a meter on the wires and test it as well. Usually a bad cat will show other signs as well. It will usually be the sensor. Also bad cats do not always smell bad (in my experience very sheldom do). I have also gotten this same code because of a bad primary sensor as well.



FU Tuning

I have a friend that has a scan tool idk what kind it is but he told me that he can read O2 sensors voltages so we'll give that a try before next week... and see what i get! is there any possibility that both O2 sensors would go bad at the same time??? and would they both jump around in voltage, or would they both read nothing at all if both bad???

Your cat is most likely shot. The sensor is just doing its job and telling you that. That's why GM put it there. The cat is there to burn anything that the engine doesn't. The fact that unburned fuel is coming out of your exhaust should have tipped you off if the CEL didn't. Cats don't ALWAYS smell like rotten eggs when they die.

2002 Cavalier 2200 5spd

Maybe the cat isn't completely dead, but if it's geared towards performance, it probably isn't doing its job as well as the stock part emissions-wise. You can either buy an O2 simulator or install a more effective read: restrictive cat.

2002 Cavalier 2200 5spd

yeah i just ran codes on it today and the O2 sensors are working properly! i guess i never really put the two together... if the cat is shot why would i buy an O2 simulator?? wouldn't still not work right? or am i not reallizing what a simulator actually does?? does n e one have any thoughts on what kinds of a cat to get (or not to get)???

What codes does it have?

I O2 sim is for the rear O2 sensor, if you were to remove the cat. There is 2 types of O2 simd. Manual and electrical. Electrical plugs into the O2 sensor plug, manual uses a stock O2 sensor.




FU Tuning

the code is PO420! I don't really want to get rid of the cat seeing as how it burns the rest of the fuel that the engine doesn't!!! well what i think i'm going to do is get a new cat and put it on seeing as how all signs seem to point to that as the problem!!

does n e one know of any good or bad cats?? i had a flowmaster, for 2 1/2 yrs... and if i'm right it is the problem, and is no good... shouldn't it have lasted longer??

should....but they dont

so its been over a month now and i never changed the cat in my car yet... money issues... but my check engine light just came on today... why did it take so long to come back on if the cat is bad??

I think that your cat is in the process of dying. I may be working properly for a few weeks and then it takes a crap. I went through this on my car for awhile to, with the light coming on and off for the same code. I replaced my cat, and I haven't had ANY CEL for well over a month now, quite an accomplishment for a 97 Cav! lol...


Aaron


97 Cavalier Z24 @ 85k
00 Cavalier Base Coupe @ 152k...rollin on 14's!
97 Grand Cherokee 5.2L@ 260k

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Quote:

why did it take so long to come back on if the cat is bad??

Do you do a lot of city driving or short distance highway driving? I think it checks the cat. conv. after driving steady on the highway and then coast to almost a stop

yeah.. i drive alota shorter trips 10-15minutes... i did notice the once i drove about 100miles then let it sit over night and when i went to go home the next afternoon the light came on like 2minutes into the drive...

I'm having the same issues right now but I replaced the CAT twice in less than 2 weeks thinking it was defective the first time and replace both 02 sensors. Still nothing works and I'm still getting the po420code saying my CAT has issue. I'm having a hard time believing 3 CATs are defective.

im having the same problem, i replaced both o2s and still no luck, i have a an aftermarket cat on for about a year now, should i replace the cat?