P0421 code

[7milesout]

My guesstimate is that rear O2 sensor should always read RICH (no oxygen) if the catalyst is working properly. If it starts moving leaner, at some threshold I suppose that means, or is deciphered by the ECU as, the cat is no good. Not a statement based on any learning, but what I estimate based on playing with O2 and AFR sensors quite a bit.

[Wallythacker]

How do I find out degree of degradation? The handheld tool I borrowed doesn’t report that.

I don't know if any tool would report it other than some expensive emissions tester like Ontario garages used to have. I recall a friend getting a fail because their cat was "partially plugged" according to the emission test center. Only way you get that it to measure the degree of failure in the cat.

It's common to have a pending and active code. I see that P0421 code relatively often on higher-ish mileage 2015 Mirages after 300,000km or so. Have the spark plugs ever been changed?
I'm not O2 sensor book learn ed. But from what I understand, the front sensor(pre-cat) is used to adjust fuel/air mixture and the rear o2 sensor is only used to tell if the cat is working properly. The rear O2 sensor normally doesn't affect how the car runs, it's there to tell if you need to pay more carbon tax or not.
I guess a guy could compare the front and rear o2 sensor outputs and if they're similar then your cat is nfg. I dunno, google could probably help out more with that. I don't believe there is a cat degradation value that exists in the ecu?

Without knowing, I'd guess there's one code for a total cat failure as determined by the ECU and another code for a "well, it's kinda baffed"

[littlemoule]

Interesting replies. Okay so since no definitive answer yet, I went ahead and reset the code. The check engine light is cleared. If it comes up again, I will be sure to post here again. So for have driven 200km, no check engine light yet. I do expect it to come on sometime. If it never comes back on then i'll assume the problem is not there anymore and that the cat doesn't need to be replaced.

[Fummins]

How many miles are on your car? Have the spark plugs ever been replaced? I'm sure it probably sounds stupid but I know someone with a pos chevy cruze that had a P0420 and replaced the cat and both o2 sensors and the code kept coming back....New spark plugs seemed to be the fix, car had over 200k kms on the originals.

[littlemoule]

Actually that's a good point, I will see if I can replace the plugs they are relatively inexpensive anyway. Car has 165000 km on it.

[Fummins]

It's worth a shot. Might be a waste of time but the book calls for plug replacement at 160k though they often last a lot longer being iridium.

[Fummins]

I had an 06 Chevy Van at work that some crack head stole the lh cat from the other night. So I chopped out the rh one and welded in a couple chunks oh pipe. Can't steal it if it's not there. Of course after a few mins of driving the check engine light came one. I just checked the codes and P0420 and P0430 are stored(cat efficiency below threshold- bank 1 and 2). The Cel coming on was expected, it's being "fixed" right now.
If anyone is curious as to what codes you'll get when your cat is at 0% efficiency, there you go. The same p0420 could be caused by something else too though...

[7milesout]

These crack-heads stealing catalytic converters ... something has got to give. This is beyond getting on my nerves hearing about. I'm lucky I haven't been a victim, yet. But something has got to be done to stop the crack-heads.

[Fummins]

These crack-heads stealing catalytic converters ... something has got to give. This is beyond getting on my nerves hearing about. I'm lucky I haven't been a victim, yet. But something has got to be done to stop the crack-heads.

Yeah it's crazy out there. Things were quiet for quite a while around work after a scrap dealer got shut down. But they just got a slap on the wrist, free room and board and free schooling if they're good. I knew a guy that used to purposely do stupid **** so he'd go to jail near the mountains each winter so he wouldn't be on the streets. It was a lifestyle for him. He even got his welding ticket in jail!

We're not replacing cats anymore unless absolutely necessary. They're getting replaced with pipe and deleted by a tuner guy in town. Until the epa or some other granola people get wind of that. I mentioned doing that about $30k in replacement cats ago. A security bear would be pretty handy to have around here.

[7milesout]

We have to do emissions testing, in the 7 counties in the local and vicinity of the Thunderdome. But I have a work around if I want to avoid doing it. I can register vehicles at my sister's address (my dad's home, where I grew up). No need to do that as yet. I just (try to) keep my cars in top shape. I try, but something is always busted.