Ok to drive with Check Engine Light on stemming from P0420 code? (CRV, buying)
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There is a universal symptom of an actual failed Cat converter. The smell of rotten eggs caused by sulfur dioxide from the failed cat. Very distinctive odor. Very offensive for drivers behind you. Otherwise, probably the upstream or downstream O2 sensor, as has already been noted.
There is a universal symptom of an actual failed Cat converter. The smell of rotten eggs caused by sulfur dioxide from the failed cat. Very distinctive odor. Very offensive for drivers behind you. Otherwise, probably the upstream or downstream O2 sensor, as has already been noted.
No, that smell has nothing to do with the catalytic converter. That smell is caused by crappy gasoline with too high a sulpher content.
Thanks for everyone's posts. Just wanted to give another update since my last post on 12/3. But before I do, when a mechanic changes out a catalytic converter, are the O2 sensors just part of the replacement CAT piece? Or are they a separate piece but they just change them out at the same time because they are in the same area and easy to do? Never understood this if someone could explain, thanks....sorry if I missed someone answering this for me earlier!
Ok so for the update. I mentioned the light came on with that P0420 code on 12/2 (by the way, when I read it on the ODB reader, it comes up as 2 codes but both show as P0420...not sure if that helps or means anything). The check engine light turned off on it's own two days later on 12/4 at 180,310 miles. For the first time, I decided to try premium gas which I got the next day on 12/5 after the light already went off to see if it would help the issue later on. I also got my oil change on 12/11...the light was still off but they hooked it up anyways and no code was stored which they mentioned is a good thing because codes can still be stored even with the light off. I got premium gas a second time on 12/15 and then a third time on 12/21. But then, the check engine light came back on this past Friday on 1/8 at 181,766 miles. I took it to Autozone the next day on 1/9 to make sure it was the same code and sure enough it showed 2 codes like always, both being P0420. I learned from using their OBD reader that I could "erase" the code myself so I did that so currently it is no longer on the dashboard but again who knows when it will come back on again. I also want to make another note that the night before the light came back on 1/8, it was rainy/cold and that morning the car was wet, etc. which seems to be a common occurrence like I've mentioned before. I got premium gas again a fourth time today on 1/10 but the premium gas doesn't seem to be fixing it.
So no idea what to do going forward. Again, I'm not a car guy so like some of the suggestions mentioned, I can't just try replacing the O2 sensor on my own first before replacing the whole CAT like my mechanic mentioned. Again, they mentioned they would look at everything first but seemed to imply they would just replace the CAT all together because they mentioned if they changed out the O2 sensor first and that wasn't it, it would just cost more in the end. It just seems ironic that the light comes on a lot of times when the weather conditions are wet, etc. Just want this problem to be done with once and for all, but just not sure how to move forward lol.
Last edited by jagsfan05; 01-10-2021 at 07:48 PM..
I called my mechanic (who has amazing reviews and has always been trust worthy) and they can't get me in for another week. They again mentioned they would probably just need to replace the CAT all together. They said it probably wouldn't just be the O2 sensors because they said if it was the O2 sensors, it would have brought up another code besides just PO420.*There's a chance that when they replace the CAT, they might also need to replace the O2 sensors too though.
I called my mechanic (who has amazing reviews and has always been trust worthy) and they can't get me in for another week. They again mentioned they would probably just need to replace the CAT all together. They said it probably wouldn't just be the O2 sensors because they said if it was the O2 sensors, it would have brought up another code besides just PO420.*There's a chance that when they replace the CAT, they might also need to replace the O2 sensors too though.
I have owned a repair shop for 40 years. I have never seen O2 sensor replacement address the problem of a P0420/430 code with no other codes.
There is a universal symptom of an actual failed Cat converter. The smell of rotten eggs caused by sulfur dioxide from the failed cat. Very distinctive odor. Very offensive for drivers behind you. Otherwise, probably the upstream or downstream O2 sensor, as has already been noted.
The smell happens when the converter is working overtime due to being overwhelmed with unburnt fuel either due to ignition misfire or improper fuel mixture. A failed converter will NOT produce the smell. High sulfur content in the fuel will aggravate the problem. If the misfire is not corrected in a timely fashion the overworked converter will fail at which time the rotten egg smell will go away,
I have owned a repair shop for 40 years. I have never seen O2 sensor replacement address the problem of a P0420/430 code with no other codes.
I'd agree. There are alot of methods of testing a cat out there.. I don't do it enough to say whether they all work or not..
There's watching the O2 sensor data, which seems to be pretty reliable. I'd honestly have to look it up because I don't recall the details. But, watching the downstream O2 sensor can give you indication of how the cat is performing. After all, this is how the vehicle is telling whether to set the code. Now, O2 sensors can go bad in odd ways. Most of the time, you lose the heater, or it just stops working, or it's wiring, all of which will pretty much always set a code.. But every now and again, you get a slow reacting O2 sensor. But, generally, in a situation like that.. You'll wind up with a rich/lean code being set. So, looking at the O2 sensor data coupled with the fuel trims should be pretty clear.
Some people will swear by measuring the temp of the cat. personally, I think this is a better test to tell if a cat is plugged than whether it's working.
Tapping into the exhaust before and after the cat and measuring pressure I think is the gold standard for telling whether a cat is plugged or not.
As for the O2 sensor and the cat that OP brought up.. normally, it's probably smart to replace the O2 sensor when the cat is replaced. Whether the downstream O2 has to be moved depends on the vehicle and perhaps whether a direct or universal cat is used.. And can have many other factors, such as how much rust there is. And then the question of whether if it has to be removed, if it CAN be removed without breaking the damn thing. In general, the O2 is generally not 'part' of the cat, it's on pipe after it that isn't replaced when replacing the cat.. But.. as with anything.. YMMV.
I'd say all in all.. It'd probably be best to plan on replacing it. In general, they're not expensive and it's no real extra work to do it while they're down there. I look at it as kinda like replacing the water pump when doing a timing belt. But.. The $70-ish for the part may be a big deal to you.
Exhaust is just a total PITA to work on. You have to plan on things taking twice (or thrice) as long as they 'should' because you're going to break out a torch to heat up bolts to get them loose. You're going to use a can of penetrating oil.. You're going to have studs break off. Exhaust is something that I gladly pay someone else to do just to save myself the headaches.
Thank you guys for your responses and help for breaking this all down since I'm not car savvy at all, especially Don in Austin's comment...that makes me feel a little better about just going ahead and replacing the CAT all together then and trusting my local mechanic. So you guys seem to possibly lean towards just replacing it and I wouldn't be making a bad decision? Is the weather conditions when this comes on not weird though?
Again, this check engine light code P0420 first came up in December 2018 for the first time and never came back until July 2020. So in June 2019 I passed emissions with no problems (didn't have to do emissions in June 2020 due to COVID). Does that tell us anything or no? Also it's not unusual that a CAT would need replacing during the lifespan of a car, correct? Just want to make sure I'm not getting the wool pulled over my eyes from that aspect if this isn't typical and out of the ordinary.
It's just tough because I can't tell my local mechanic what to do in regards to "testing the O2 sensors" out first...everytime I bring it up they have some type of reason for not doing that such as they can't do that or if it was O2 sensors they would bring about another code. So they seem pretty set on just replacing the CAT all together. It's frustrating because they are trust worthy but I just can't get through to them on this. I've called a Volvo independent shop in another close by city and they brought up what you guys mentioned that it could be just O2 sensors which is what they can try replacing first before replacing the whole CAT...but I don't know them as well or how trust worthy they are. Just so confused on who to listen to or what to try to end this problem once and for all! Again, I've never noticed any type of egg smell if that's a for sure symptom of a CAT needing to be replaced though?
Sidenote, my wife was leaving work three days ago on 1/13. She got in the car, turned the key and it got stuck plus the car wouldn't start up. She managed to get the key out but she was noticing the car wouldn't respond by locking/unlocking and tried again to start it back up but nothing was turning on. Sure enough, we got AAA to come out and they tested the battery which was dead. It was purchased back in May 2017. We replaced it with AAA for a new battery. Surely this wouldn't have anything to do with the check engine light/code P0420 after all these years right? I'm sure it doesn't because the first time this issue came up was in December 2018 and never came back until July 2020, just thought it was worth mentioning.
Also, if I replaced the CAT for say $800-$1000...is it still worth it in terms of how much life the car has left? Again it's a 2008 Volvo S40 with 182,000 miles roughly on it. How many miles could I expect to get out of it? Really not wanting to move on from the car yet if I don't have to but also don't want to waste money. But even if we didn't want to change out the CAT and move on from the car in the future...would we still have to replace the CAT first before we got rid of it? I thought I saw someone post on here that it's considered fraud to try and sell or trade a car in without addressing all the issues first?
Last edited by PJSaturn; 01-16-2021 at 04:08 PM..
Reason: Edited at user's request.
What you need to do is go to a Volvo forum.
They will have all the answers you need, as many of them will have gone through the same thing with such an old car.
Thank you guys for your responses and help for breaking this all down since I'm not car savvy at all, especially Don in Austin's comment...that makes me feel a little better about just going ahead and replacing the CAT all together then and trusting my local mechanic. So you guys seem to possibly lean towards just replacing it and I wouldn't be making a bad decision? Is the weather conditions when this comes on not weird though?
Again, this check engine light code P0420 first came up in December 2018 for the first time and never came back until July 2020. So in June 2019 I passed emissions with no problems (didn't have to do emissions in June 2020 due to COVID). Does that tell us anything or no? Also it's not unusual that a CAT would need replacing during the lifespan of a car, correct? Just want to make sure I'm not getting the wool pulled over my eyes from that aspect if this isn't typical and out of the ordinary.
It's just tough because I can't tell my local mechanic what to do in regards to "testing the O2 sensors" out first...everytime I bring it up they have some type of reason for not doing that such as they can't do that or if it was O2 sensors they would bring about another code. So they seem pretty set on just replacing the CAT all together. It's frustrating because they are trust worthy but I just can't get through to them on this. I've called a Volvo independent shop in another close by city and they brought up what you guys mentioned that it could be just O2 sensors which is what they can try replacing first before replacing the whole CAT...but I don't know them as well or how trust worthy they are. Just so confused on who to listen to or what to try to end this problem once and for all! Again, I've never noticed any type of egg smell if that's a for sure symptom of a CAT needing to be replaced though?
Sidenote, my wife was leaving work three days ago on 1/13. She got in the car, turned the key and it got stuck plus the car wouldn't start up. She managed to get the key out but she was noticing the car wouldn't respond by locking/unlocking and tried again to start it back up but nothing was turning on. Sure enough, we got AAA to come out and they tested the battery which was dead. It was purchased back in May 2017. We replaced it with AAA for a new battery. Surely this wouldn't have anything to do with the check engine light/code P0420 after all these years right? I'm sure it doesn't because the first time this issue came up was in December 2018 and never came back until July 2020, just thought it was worth mentioning.
Also, if I replaced the CAT for say $800-$1000...is it still worth it in terms of how much life the car has left? Again it's a 2008 Volvo S40 with 182,000 miles roughly on it. How many miles could I expect to get out of it? Really not wanting to move on from the car yet if I don't have to but also don't want to waste money. But even if we didn't want to change out the CAT and move on from the car in the future...would we still have to replace the CAT first before we got rid of it? I thought I saw someone post on here that it's considered fraud to try and sell or trade a car in without addressing all the issues first?
Let me repeat, rotten egg smell is NOT an indication that the catalytic converter needs replacement.
For the problem to be intermittent and borderline with the check engine light and fault coming and going is not at all uncommon. I have heard of cases where the code only set @ high altitude and then eventually went away until the next trip to the mountains.
You can try the O2 sensors but I have never known this to fix the problem. Without O2 sensor fault codes, there really is no testing to be done for them.
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