Ok to drive with Check Engine Light on stemming from P0420 code?

[Don in Austin]

Here is why weak or failing O2 sensors -- the upstream being of enhanced design and referred to as air/fuel ratio sensors on modern cars -- are unlikely to cause catalytic converter efficiency codes without O2 sensor codes.

The powertrain computer looks for the converter to store and release oxygen as the oxygen level into the converter fluctuates. So the converter is judged working if the ratio of fluctuation level is greater at the inlet than the outlet of the converter as monitored by the sensors. As a sensor fails it becomes less responsive. If the downstream sensor were to become unresponsive it would, if anything, judge the converter MORE efficient than it actually is. If the upstream sensor becomes unresponsive there is a code that will set for that based on the computer's calculations of its continuous fuel/air ratio corrections.


Codes for lazy upstream sensors are common. They are not normally accompanied by converter efficiency codes.

[jagsfan05]

Thanks Don! Could the bad battery that I had to replace last week also be anything to do with why the Check Engine Light/P0420 code has been coming up the past few years or probably not? Just seeing if I should still lean towards replacing the CAT or if a bad battery had a chance of causing all this to begin with but I doubt it.

I called my mechanic and they said the bad battery problem probably wouldn't be the cause of the P0420 code. So frustrating on who to believe with different answers not corresponding.

They also told me if I go with changing out the CAT, my options were:
1. Genuine Volvo for $1496
2. Magnaflow (which is considered OEM grade. But they said it was confusing because on one page it didn't say OEM and another it did) for $1250
3. Bosal for $860

Again I don't know anything about cars so would you guys recommend one of the three the most? They said they would have just done Magnaflow but just wanting to make sure. Also I'm confused because I thought aftermarket and OEM were two different things but aren't Magnaflow and Bosal aftermarket? Yet Magnaflow is OEM grade?

[Labonte18]

Originally Posted by jagsfan05

Thanks Don! Could the bad battery that I had to replace last week also be anything to do with why the Check Engine Light/P0420 code has been coming up the past few years or probably not? Just seeing if I should still lean towards replacing the CAT or if a bad battery had a chance of causing all this to begin with but I doubt it.

I called my mechanic and they said the bad battery problem probably wouldn't be the cause of the P0420 code. So frustrating on who to believe with different answers not corresponding.

They also told me if I go with changing out the CAT, my options were:
1. Genuine Volvo for $1496
2. Magnaflow (which is considered OEM grade. But they said it was confusing because on one page it didn't say OEM and another it did) for $1250
3. Bosal for $860

Again I don't know anything about cars so would you guys recommend one of the three the most? They said they would have just done Magnaflow but just wanting to make sure. Also I'm confused because I thought aftermarket and OEM were two different things but aren't Magnaflow and Bosal aftermarket? Yet Magnaflow is OEM grade?

Where are you again? And are those prices for the cat or the cat plus installation?


Because.. RockAuto.. The Bosal cats range from $277 to $440 for the part.. And those are non-CARB compliant. They have one Bosal CARB compliant that is $1134.89



That's really the question that needs to be asked. I suspect that if those prices are parts only, that the Volvo and Magnaflow are CARB compliant while the Bosal is not.


If it is NOT CARB compliant and you're in or near New York, Colorado (Didn't know that one), California or Maine.. You will have issues. if you sell the vehicle to someone in those states.. There'll be issues. Now, I hope that you are NOT in those states because if you are and your mechanic quoted a non-CARB compliant, something's really wrong. But, it's something you need to be aware of because it can affect your resale of the car, should you ever want to do it.

I'll add here that what i'm seeing on the parts, it seems Volvo may have MANY different cats for this vehicle. So.. Certainly getting the part from Volvo matched to the VIN.. there's some logic in that.

[jagsfan05]

Labonte18 thanks for the reply. They didn't tell me if they were CARB compliant but I could double check. These quotes are prices for just the CAT...not installation included. I live in TN. Also you mentioned this car has more than 1 CAT? But my mechanic hasn't said anything about that?

So just an update....Again looking at my notes from the printout code it gave me at Autozone all these times said "Catalyst efficiency low-bank 1 Explanation The oxygen sensors monitor the Catalytic Converters ability to store oxygen" and goes on to list probable causes. Not sure if that helps.

I took the car into my mechanic this past Tuesday on 1/19. I told them a week ago that the light came back on 1/8 but hasn't been on since 1/9 because I cleared it myself at Autozone. They had the car all day and called me saying that the good news is the light isn't on...but I'm frustrated because I knew it wasn't on and told them that. They must have forgotten. They said without the light on they couldn't really tell much but even with the light on...they can't really test the CAT out to see if it needs replacing. They said if it were them they wouldn't put the money down to replace the CAT right now because they also don't want it coming back on them if that doesn't solve the issue. They said it shouldn't be a problem driving especially if emissions isn't due and if I'm not noticing any problems. Again...no I'm not noticing the smell but I feel like I am noticing a lack of quicker acceleration, especially going up hills which I said to them. They said they could change out the CAT if I wanted to but you can tell they just don't seem confident. They are very nice though because they were just saying they felt bad me putting that much money down so you can tell they aren't just trying to take my money.

They also said my situation with how the light comes on and off the past few years seems odd because usually they just clear the code for people and it stays off or comes back on and stays on. I had to reclarify that the issue came up for the first time in December 2018 and didn't come again until July 2020 but more often since then which just seemed abnormal to them. But from my research, the P0420/CAT code acts just like my situation for others so that makes no sense to me. They also said another idea would be to take it into the Volvo dealership for their confirmation and then if they confirm it they could do it for me. But they also said the Volvo dealership wouldn't be able to tell any additional information either without the light on....so now I feel stuck. I can't predict when this light will go on and off and even so if you can't tell for sure the CAT needs replacing when the light is on like they said...how will this help. So now I'm super frustrated because I have no idea how to proceed especially if they aren't confident anymore when they were all along until now. Every other time the past 1-2 years when I tell them the code I'm getting back, they said it's probably the CAT needing to be replaced. Plus when I took the car into them back in August with the light on, they just cleared it that day. So they had the opportunity to check it out then with the light on. They told me on this past Tuesday if the light comes on again, it might make them feel more confident which makes no sense to me because it has constantly been coming on and off the past few years and I can't guarantee bringing it into them with the light on.

I understand a lot of you will say don't worry about it and to not fix anything. Usually I would believe you but the fact this keeps coming back makes me believe something needs fixing. Plus it's been 2 years now which worries me more. No idea how to move forward now. I obviously don't want them replacing it based off just my opinion because I don't know anything about cars...I want someone confident to say that's what it is and to move on from this. So fed up with this.

[Labonte18]

Originally Posted by jagsfan05

Labonte18 thanks for the reply. They didn't tell me if they were CARB compliant but I could double check. These quotes are prices for just the CAT...not installation included. I live in TN. Also you mentioned this car has more than 1 CAT? But my mechanic hasn't said anything about that?

I didn't say it did.. but.. It wouldn't surprise me. But don't let this confuse you here.


Most newer vehicles have what is often referred to as a Pre-CAT. this is a catalytic converter that is integrated into the exhaust manifold. (A V-6 or V-8 could have TWO pre-cats, then the main cat for a total of 3!) If THIS CAT has to be replaced, you generally have to replace the entire exhaust manifold. I haven't seen one yet that could be replaced without replacing the manifold, though that certainly doesn't mean they don't exist. If THIS converter fails, there's also a different code set due to it being above the top O2 sensor. Personally, I've never seen one of these fail due to the catalyst.. It's always been a weld failing or the exhaust manifold itself failing.




What I said was that there are multiple DIFFERENT CATs available for this vehicle. Just looking at RockAuto, because.. I am NOT an expert on Volvo.. Hell, I won't even qualify myself as an expert mechanic. But when I see things at Rockauto when looking at the catalytic converters that say "Engine Code B5244S4; Ultra Low Emission Vehicle (ULEV)" and "Engine Family Number 8VVXV02.4U2N".. That kinda tells me that they have used different catalytic converters for different options on the S40. And it can make life a living hell matching up the right part. Because, if you have engine 8VVXV02.4U2N, you don't want to put a CAT for engine code B5244S4 on it. Because it's not the right CAT.


That's why I said that there is some good sense in buying a genuine Volvo part. Because Volvo will get the VIN and know EXACTLY which CAT goes with this vehicle. Plus.. I haven't seen a manufacturer yet that sells a non-CARB compliant CAT. That's not to say they're not out there, but.. It would surprise me.

With you being in TN.. Really there probably shouldn't be an issue so far as the CARB compliance. I think you all are the same as us here in SC where as long as it has at least 3 of the 4 wheels on it.. It's OK. No inspections or anything.

But.. Were you to move to one of the states I listed before.. You could have problems passing emissions. Or, if you sold the car to someone in one of those states. Not saying it's something you should be worried about, but it certainly is something that you should be AWARE of.




The long story short version.. As I'll bet Don will attest to.. There's sometimes things that mechanics just refuse to accept as the truth.. One of them is "New does not mean good". Anyone who's gotten a bad part out of the box can attest to this.. and then there's the customers who say the wheel speed sensor was "Just replaced".. 200k miles and 15 years ago.

Another is "Direct Replacement is an oxymoron". And CATs are a very, very persnickity part. I know on my truck, there's a cat for the 4 cylinder and a different for the 6 cylinder. Well, obviously, that makes perfect sense. But, there's one for 2WD and another for 4WD. There's a different cat if you have the off road package. There's a different CAT if you have the sport package. Especially with cats.. It's virtually impossible to say "I need a part for a XXXX vehicle".. Because they change the parts with the various different options and packages.

[Mr78609]

Originally Posted by elnina

Yes. You are safe. It's just for the environment.
Enjoy the drive and don't worry about. Ask your mechanic to disable the engine light. It's annoying...
Merry Christmas!!

I thought that "tampering" with the OBD 11 system was against federal pollution guidelines and against the law//// Is this not so? thanks

[jagsfan05]

I understand some people's points about ignoring and not worrying about this check engine light. But if the light keeps coming back...isn't that indicative that something is wrong? I've heard people have bad CATS even with the CEL coming on and off...not just staying on all the time, no? I'm just curious how we would know that the CAT does need to be fixed and aren't these are all signs? I mean, I have noticed what I believe is maybe a little less quicker power/acceleration putting my gas on the pedal when merging on interstate, etc and from what I hear this is one symptom.

So just another update. Check engine light came back on 2/12/21 @ 183,296 miles when it was roughly 28 degrees out that morning, took it to Autozone and again confirmed code P0420 like always. We had a snow storm in our area a few days later so the car wasn't driven for a week and once we started driving it again on 2/22/21....the check engine light went off on 2/24/21 @ 183,544 miles when it was roughly 65 degrees out. I'm kinda frustrated because when the check engine light came back on 2/12, I called a second mechanic and set up an appointment on 3/2 to bring it in just to see if they could determine anything with the issue. They told me that they would prefer the check engine light being on in order to help diagnosis it better....but of course the light went off on 2/24 so now I have no idea whether I should bring it in or not because it could be a waste of time with no light on. I also was doing nothing but premium gas for almost 6 fill ups hoping this would fix the issue but the check engine light came back on 2/12 so I'm done trying that out because it obviously didn't work. This second mechanic said they do use VIDA while my first mechanic said they do not and only use Autologic and Autel which has most Volvo things but not all. If you recall, one time I took the car in to my first mechanic with the light off and they said no codes were stored which is a good thing because codes can still be stored even with the check engine light off.

So just another frustrating update and not sure how to proceed. I understand that I might should just not worry about it but I'm also not a risk taker so something worsening scares me too. Hope these updates help someone.

[toore]

My mechanic said that cat. converter needs to change after p0420 code. So i ordered $760 bucks new one (2017 honda crv) from amazon, my milage is nearly 80K miles, so i need to replace it with the new one.
when i check it from [url]https://p0420.net[/url] , it says the code may occur from cat. converter and o2 sensor. What should i do now ? should i change the sensor also ??

[dkf747]

Originally Posted by toore

My mechanic said that cat. converter needs to change after p0420 code. So i ordered $760 bucks new one (2017 honda crv) from amazon, my milage is nearly 80K miles, so i need to replace it with the new one.
when i check it from https://p0420.net , it says the code may occur from cat. converter and o2 sensor. What should i do now ? should i change the sensor also ??

I think you should go back and read all of Labonte18’s posts in this thread. That will help you find the answers you seek.

[BostonMike7]

Incorrect air/fuel mixture can also cause a P0420 code. That could be due to a few things such as vacuum leaks, misfires and other issues with the engine.

So while the codes is usually cat or O2 sensor related, I wouldn't start off firing the parts cannon at the problem. It still would behoove one to do some troubleshooting on the engine to determine if the cause of the code is further upstream of the O2 sensor/cat.