I noticed I had just hit 160,000 miles and about 5 miles after that into my drive the check engine light came on (Code P0420). Do you think this is more of a maintenance reminder than an actual problem and if so how do I get rid of it? Or could this be a indication of something more serious? No display messages came up like "Book Time for Maintenance". Only the check engine light.

Everything seemed to be running fine with no issues when this came up. Thanks for your help (FYI I don't know much about cars at all)

 

best start by reading the owners manual on the difference between the service interval light and the check engine light (if you don't have one, simply google "volvo 2008 s40 owners manual" to find the online version. If it is indeed the service interval light, you can reset by doing the following:

1. Press and hold trip reset button,
2. turn on the ignition,
3. wait for the yellow warning light to start blinking,
4. release the button and wait for confirmations sound,
5. turn off the ignition,
6. turn the ignition back on to check if the service message is gone.

If it is actually a check engine light, you need to have a shop scan for error codes to tell you what's at fault (or go to an Autozone and borrow an OBD2 code reader then post up the CEL codes but given you're not hands on, I'd just ask your shop to check for the fault codes.

 

It is an indicator of a fault, not a maintenance reminder.

 

Thanks so much guys! Yeah, no display message has come up...only the check engine light. So I went to an Autozone just now because my local mechanic can't fit me in yet. The code came up on their side as "PO420", that's all he told me. Any idea what this means and how serious it is?

I was hoping to drive 214 miles down and back to my family's house (428 in total) this weekend for the holidays but a little nervous if my mechanic can't get me in today or tomorrow. Thank you!

EDIT: I just called my independent mechanic who is pretty trust-worthy I believe. I told them the code and they said it's the catalytic converter that's needing to be replaced...$800 for the part and roughly $150 in labor so about $1000 in total. UGH....I hate this. They said it wasn't urgent because my emissions isn't due for another 6 months but I wouldn't want to wait on it because something could burn up? Couldn't remember what they said. They said I'm still fine driving the car with no problems and could just wait to do it when I get my next oil change with them in 2,000 miles. I might just take it to them in the morning to get it done for peace of mind since I'm driving 200 miles this weekend out of state. I called my old mechanic back in CA that only works with Volvos and he agreed with the assessment. He said when he gets this code, he just replaces the catalytic converter and that it's more than $1000 out there.

SECOND EDIT: My mechanic said they had too many spots booked in the morning and wouldn't be able to fix it before my trip. So I hope I'm ok driving it?

The only other issues my car has been having was a couple weeks back the car wouldn't start up and read a display message of "Immobilizer Try Start Again". I tried starting the car up 3-4 times after that with no luck but then my wife accidentally slammed the glove compartment shut. After that, it started up just fine and I haven't had any problems with it since. I've heard something down under the glove compartment could get loose and cause that problem until you re-attach it. My wife hit a pothole the day before she told me so maybe that caused it. But I brought this up to my mechanic and they said this wouldn't have anything to do with the "P0420" code.

The only other issues besides that is maybe low acceleration but maybe it's always been like that and it's in my head.

Your thoughts?

 

The P0420 code is saying the catalytic converter is not operating at full efficiency. The cause can be one of several things - a bad catalytic converter, one of the oxygen sensors is off (there's two O2 sensors and the code is based on a calculation between the front and the rear sensor. The front sensor also does the fuel trim so if you have an intake air leak or exhaust leak it can mess with the calculation as well. usually when you put in a new catalytic converter, the shop will also put in new O2 sensors (since they bolt in).

I'd agree with the assessment that its not an urgent fix until you need to get the emissions test so you will have time to shop for your own parts and still drive the car. You can check out mail order Volvo dealers for discounted Genuine Volvo parts or shop a Volvo friendly online parts store to save on the parts (I'm on the east coast so I use Tasca parts (dealer), FCP Euro and EEuroparts. There's some good providers out west too including IPD USA, AZ Autohaus etc.

As to the start again issue, I think your model does have a CEM under the glove box that if the cables aren't fully seated the car can act up. Intermittant issues are hard to diagnose so you may have to wait for the next fail.

 

Thank you for your reply. Again, they just kept saying that if it was the O2 sensor that it would bring up a different code. They said they'll do tests and won't just completely change out the catalytic converter right away but I'm not sure. So am I right in assuming when you replace the catalytic converter it also replaces out new O2 sensors? Again I don't know cars and that's what she and someone else seemed to imply? Because I thought from what I understood changing out the CAT changes out all the O2 sensors for new ones as well? That's what I thought I was told. Because that's why they recommended just changing the whole CAT out rather than guessing which O2 sensor it is which could be more costly. They said each 02 sensor to replace for them is $250. How many O2 sensors is there on my car by the way that they are referring to?

In all fairness to this local family mechanic, there have been repairs that I've been told that needed to be done by other mechanics that this local family mechanic business said didn't need to be done. So they aren't always just trying to take my money it seems.

Also, am I save driving the car in the mean time? Do I need to ask them to disable the engine light before I go on my trip? They mentioned they had time tomorrow morning only to try resetting check engine light but also said it would probably just come right back up (they don't have time tomorrow to fit me in to do the repair).

Is there any difference in driving with the check engine light on for this code or do I need to have it reset/cleared in order for the driving to be safe that you mentioned? Because if the check engine light being on makes no difference I might not go by their shop tomorrow morning in order for them only to "reset" the check engine light.

Also, how long do you think I have until I need to get this fixed? Is the 2000 miles until my oil change too long of a wait? Thank you for your suggestion of shopping for new parts but again I'm not a car person and don't trust myself to buy my own parts, etc.

 

yes there are codes for O2 sensors that's true - ie if the sensor opens circuits or shorts there's specific codes, if the fuel trim goes off out of range there's a different code. So if all is normal, then the 0420 points to the catalytic converter. You can search for other posts on people who had this code to see that its not 100% certain. Here's the tech guide readback:

P0420 = ECM-4801
Diagnostic trouble code (DTC) information
Condition
The control module continuously checks three-way catalytic converter (TWC) efficiency by comparing signals from the rear heated oxygen sensor (HO2S) with the front heated oxygen sensor (HO2S). Diagnostic trouble code (DTC) ECM-4801 will be stored if the efficiency of the three-way catalytic converter (TWC) deviates too much.
Substitute value
Rear heated oxygen sensor (HO2S) control is disabled.
Possible source
-misfiring
-air leakage in the intake system
-air leakage in the exhaust system
-faulty fuel pressure
-uneven compression
-defective three-way catalytic converter (TWC).
Fault symptom[s]
-malfunction indicator lamp (MIL) lit.

The code can be set due to a temporary condition - say driving in the rain and something gets wet or the cat isn't fully warmed up. So considering the cost for a new cat, it may be worth doing some simple tests like checking for intake air leaks, clear the code and see if it returns, listen and feel for exhaust leaks etc.

 

From my experience, you're gonna need the cat. Good idea to replace the oxygen sensors at the same time though.

 

I'd add that O2 sensors do fail, so since they're a LOT cheaper than a new cat, it's usually a good idea to swap out the rear O2 sensor and see if that fixes the problem. It's not a hard DIY job at all. Swap out the sensor, reset the OBD error code, and see what happens.

I checked Rockauto and there are several cat options that are a LOT less money than the $800 quote. I guess I'd be very tempted to try to save some money on a cheaper cat on a 160,000 mile vehicle. I might even try a can of the "guaranteed to pass" cat treatment. It's not expensive, and I've read quite a few user reviews (on Amazon - where they're less likely to be faked) that make it look like the stuff might actually work sometimes.

 

Hey everyone, just an update. So if you recall, the check engine light with the PO420 code came on at 160,000 miles. The check engine light actually went off at 160,153 miles. Now I was told by my mechanic and others that it would probably just come back but it still hasn't and I'm now at roughly 162,300 miles. So it's gone an extra like 2,000 miles or more with the check engine light not coming back on...do you think I'm safe or is there a high probability it will come back on?

The only thing I've started to do a better job with recently around that time when the check engine light went away is making sure I do several clicks when I close my gas cap instead of just doing one click which is what I used to do. I'm sure that has nothing to do with it but found that interesting...I'm asking now and providing an update because I'm going to get my oil change this week and need to decide if my mechanic should change out the catalytic converter still like they mentioned they probably would need to do? Besides that the car is seemingly running fine, no smells, etc.

(Again, please note I'm not car or mechanic savy...don't know much anything about cars). Sidenote, I found this article which was pretty interesting talking about it not coming back because they tried using higher grade available gas: https://axleaddict.com/auto-repair/c...verter-repairs

 

My advice: "If it ain't broke, don't fix it".

If the CEL doesn't come back on, there's no reason to be concerned about anything.

 

It never hurts to clear CEL codes during diagnostics - if something is truly broken, they will simply reset. As noted, air leaks can cause the O2 sensors to overshoot the mix which can mess with emissions - but normally a bad gas cap seal will set off an evap system code. Not a bad idea to change the gasket on the cap from time to time. I'm also wondering if your code was set on a rainy day. The cat needs to heat up to something like 500 degrees to work to spec and if not, you get a code.

Also I dunno about some of the answers in that article - the person who wrote up about it may be bad to use premium gas had his science backwards. The different of premium vs regular is that the higher the octane rating (ie 93 vs 87) the higher the resistance to ignition by compression (or an overly hot combustion chamber due to a lean mix)- thus less pinging. Modern engines have knock sensors which retard the spark to cool the combustion which is why you can run regular in most cars including Volvo turbos which "recommend" 91 without regular gas damaging the engine. The one thing about premium is that name brands typically have more additives and detergents to clean the intake and injectors. It only takes about 1-2 tanks to get the benefits of the cleaning or you can throw in a can of injector cleaner like Techron from time to time. I usually just do a fill up one a month or two with premium to help keep things clean.

 

Hmm, you mean when the AutoZone guy checked the check engine light and came up with that code? Now that you mention it, it was overcast and kinda rainy that day when he did it? So you are saying if that was the case, there might not be anything wrong with the catalytic converter? If not, what would that check engine light have come up for?

So should I be not concerned that anything is wrong with the catalytic converter going forward...especially if that CEL light doesn't come back on? What do you think the chances are of it coming back on if it's now been roughly 2200 miles since it went off? Just still a little concerned going forward.

Thanks!

 

It's impossible to say why the CEL came on and why it went off... FWIW, if it was my car, I'd just ignore the fact it ever happened at all and drive it like normal. It could have been a myriad of things that caused the original CEL, and that circumstance may or may not ever happen again. There's literally nothing to be "concerned about"... if it does come on, it's not going to "hurt anything". Even if you do end up needing to replace your catalytic converter, changes are overwhelmingly high that it won't affect anything other than the CEL coming on. Oh, and getting the car through inspection, of course. ;-)

 

Hey everyone,

Just wanted to update everyone on this topic I created. I mentioned everything above in earlier posts but as I mentioned, the check engine light originally came on in 12/2018 at 160,000 miles with the P0420 code. It eventually went away just 153 miles later and never came back on again so I had never had anything fixed. In 06/2019 I passed emissions here in TN with no issues.

But the check engine light came back on again this past Friday, 7/31/20 at 175,700 miles. I took it to Autozone to again read the code like last time and sure enough it came back as the same one, P0420. Now I have no idea what to do, lol. Keep in mind, I'm not car savvy! Reminder, this is a 2008 Volvo S40. I've mentioned up above what my mechanic has said in the past about this issue when it first came up if that helps. I'm hoping that I can keep driving the car in the meantime, but now that the same issue has seemingly popped up a year and a half later, I'm a little worried on what I can/can't do...

By the way, 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.

Thanks for any help.

 

You have 2 oxygen sensors. One before the cat convertor and one after the cat convertor. The 1st one controls fuel trims which means the car's computer uses this O2 sensor's information to adjust the fuel flow so that the car runs perfect. Now the 2nd O2 sensor is after the cat. It's job is to report how well the cat convertor is converting the car's dirty emissions into cleaner emissions.

Realize O2 sensors wear out over time. You replace the 1st O2 sensor to make sure the fuel is being correctly programmed by the computer. The 2nd O2 is replaced after reporting the P0420 code to make sure it's not reporting falsely on the very expensive cat convertor.

In states with no emissions testing it has been rumored that people of less than reputable mechanical skills use an Oxygen Sensor Spacer to move the 2nd O2 sensor away from the exhaust so that it never ever sets that stupid P0420 code again. Ever. But that's just a rumor.

https://www.ipdusa.com/products/8656...cer-ipd-109553

 

Look through the rest of the thread - the same things still apply to that P0240 code. You can try a bottle of cat cleaner (along with a high-speed road trip, preferably). If the cat is just "dirty" that might clean it up for another year or two.

Or replace the (relatively cheap) post-cat O2 sensor. Or install a spacer under it (read all about it in the previous responses).

Or, you can hand your mechanic a nice, thick pile of $100 bills and trust that it really DOES need a new cat (maybe it does, maybe it doesn't).

 

Hey everyone,

Just wanted to post an update from my last message on 8-2-20 regarding this problem with the CEL and code P0420. Regarding my last post, the CEL with code P0420 came back on 7-31-20 @ 175,000 miles. It then turned off on it's own a few days later on 8-4-20 @ 175,800 miles. But then it came back on 8-22-20 @ 176,426 miles. I took it to Autozone and again the code was still P0420 every time. I noticed the day before this on 8-21, it was rainy which seems to be a trend of when the light comes on. So after this, I took it to my same mechanic on 8-24-20 @ 176,499 miles with the light still on. They reset the light and again mentioned if it comes back on, they might just need to replace the catalytic converter like mentioned when it first came up in 12-2018. Again, as you can see from my previous messages, they aren't really up for the idea of changing out just the O2 sensors because they said it would have thrown out a different code too and that the O2 sensors are part of the changing out the whole catalytic converter and I would receive new ones so rather than just guessing and costing more money, to just replace the catalytic converter all together. So anyways, they decided to reset the light and see if it keeps coming back. They also recommended trying premium gas for 1-2 fill ups and see if that helps out? From my understanding if you do this, you have to do it though when the tank is almost empty and less than half full? I guess that's still safe to do in this 2008 Volvo S40 right? Also, I know some people have recommended an injection cleaner too but I've also heard from someone that said premium gas works like an injection cleaner so just doing premium gas would be enough to try....just want to make sure it's safe to put premium gas in my car, I know it sounds stupid but I'm not a car guy and always just done the cheapest, unleaded stuff and don't want to mess anything up.

Anyways, the code stayed off until just this week on 12/2/20 @ 180,180 miles. The code was again P0420. The morning of the day this happened, we had to defrost the car from ice overnight and it was 22 degrees out that morning when the light came back on. So again, it's a weird trend of it being bad weather when this code comes on whether it's rainy, hot, super cold, ice melting in this case. I just find it super ironic that the light/code has only come on whether it's the time of August (hot temps) or December (cold temps) in addition to the possibly rain/wet conditions sometimes. Almost like something to do with moisture at times. So overall this has been going on 3-4 times since 12-2018 and I have no idea what to do anymore. I don't know if I should just replace the catalytic converter or not. I guess I could try the premium gas trick because I never tried it after her suggestion in 08-2020 because the light stayed off for 4 months. I guess I could try to do the premium gas just want to make sure it's safe to do in my car. I also am just scared I'm doing more damage if this catalytic converter really needs to be changed out and I've been holding off all this time? But at the same time, all mechanic shops I call seem to want to just replace it and not try simpler fixes....so I feel stuck with this being $1000 to fix. I've also heard lots of stories from people online that get the CAT replaced and the light still comes on and doesn't fix the problem. Not sure if the car is still safe to keep driving after this issue keeps coming and going over 2 years. I've been trying to do a better job of making sure the gas cap has several clicks wondering if that's the issue but I guess it's still happening. The car seems still to be running just fine after all this time though but again not sure the hidden damages it might be doing. Like some people mention that a CAT shouldn't need replacing at all during the lifespan of a car so it's hard to know who to believe. I know some people just leave the code and decide not to fix it and everything works fine....but then others mention how you shouldn't let it go without fixing so I'm just confused on what to do and how much harm I'm doing...thoughts? I'm not car savvy at all so please forgive me! Thanks everyone!

 

idea behind the premium gas trick is that name brand premiums (ie Mobil, Texaco, Shell, Exxon etc the ones with the brand name additives) have extra detergents in them which can clean up injectors, valve deposits etc. In fact Consumer Reports did a test and reported it takes just 1-2 tankfuls to get the benefits of the extra detergents. You can also opt to throw in a can of injector cleaner like Techron - same concept. Seeing your fault light being set on rainy days makes total sense to me. The cat needs to heat up to an optimal operating temperatures to burn off the excess HCs so if the cat is cooled by road spray it will lose efficiency. If your sensors are right on the edge of not meeting the ECUs criteria, that cooling can be enough to set off the CEL code. Keep in mind intake air leaks and exhaust leaks or worn O2 sensors can contribute to the low efficiency reading (basically the ECU calculates a differential between the front and rear sensors) and if the rear has too much O2 relative to the front, the CEL code get set. BTW, one option to avoiding or delaying the CEL is you can insert a CELBOSS device - its a spacer that goes between the rear O2 sensor and the port, which moves the sensor away from the airflow and as such will induce a lower O2 reading...

 

I'd add that there's no reason to WORRY about driving the car. The post-catalytic converter O2 sensor is there only to test the efficiency of the cat, so the CEL is just indicating that the sensor is suggesting that the cat isn't working up to spec.

Maybe it is, maybe it isn't, but either way, it's not going to leave you stranded along the road.

Your mech would love to change the cat(s) and the O2 sensors for two reasons...
1) He makes a lot of money doing that, and
2) He gets to use your money to shotgun the problem so he doesn't have to do the diagnostic effort to determine which of the two is actually bad.

Thing is, O2 sensors are suspect when they have over 100,000 miles on them. They're also MUCH cheaper and easier to replace than a catalytic converter, so if there's any chance at all the problem is just the sensor, swap it out. For example a NTK 25646 O2 sensor is going to run you $60-70, and shouldn't be difficult at all to change out. Might fix your problem, and even if it doesn't, you have replaced a part that could have failed due to having so many miles.

The spacer suggested in mt6127's post above is another valid suggestion that I've seen work many times.

There are also products that claim to be able to clean a catalytic converter - you just pour a bottle of the stuff in the gas tank. I've seen that work on several vehicles, though sometimes the effect is temporary. Sometimes just taking a long interstate road trip is all that it takes. This all might work if your problem is contaminated media inside the cat, which typically happens if you have a misfire (so too much unburnt fuel reaches the cat), or if there is any oil blow-by (due to worn piston rings). The fact your problem comes and goes makes me think that it could be contamination, so the cleaner / premium fuel with additives, or just a road trip might well help. Since it's the cheapest and easiest thing to try, why not? Just make sure the product is specifically designed to clean cats, and NOT just "fuel systems" (a laudable concept, but won't help your problem). The other related thing is that if your high-mileage car has the original plugs, it could have excessive misfires, so swapping the plugs (cheap and dead easy) could well prevent future occurrences of your cat problem (since there would be less build-up from the unburnt gas inside your cat). And spark plugs are cheaper than the gas they'll save with improved performance, anyway (especially with the kind of miles your car has).

And FWIW, it looks like there are a host of replacement cats available aftermarket in the $300 range. Yes, that's without installation, but it looks to be a straightforward bolt-on job that any half-wit with a set of wrenches could do with ease (meaning I could). ;-)