P0420 - or - P0430 - o2 sensor or catalytic converter

[colinnwn]

My Pathy threw a P0420 yesterday. I found that means the bank 1 front catalytic converter is operating below expected threshold. It determines this by comparing the switching frequency of the front o2 sensor to the back o2 sensor, and if the back o2 sensor is switching approximately less than twice as fast as the front one, it throws the code.

 

Among the top causes, the first 2 are a defective cat, or a defective upstream o2 sensor.

 

I was wondering if there was a consensus on which was more likely to fix it, the o2 sensor or the cat?

 

For anyone who has had to replace the front cat, have you had success with one of the much cheaper RockAuto direct replacement cats? Was it very difficult to replace yourself? I have air tools. But I don't have a lift and don't want to have to go cutting into anything or welding. If it isn't a drop in replacement I should probably leave to an exhaust shop.

 

I cleared the code, and in the last 4 trips it hasn't come back yet. I haven't tried resetting all the ECU trims yet, if that is even possible without a NISSAN CONSULT. But I want to be ready to go with a plan of action for when it comes back.

 

Thanks. 

[Sjackson2]

Well if it’s throwing a code for only one side...you could try removing the o2 sensor from the side not throwing the code and swapping o2 sensors and seeing if the code follows the swap 

Edited February 14, 2019 by Sjackson2

[QuasarDecimari]

Well if it’s throwing a code for only one side...you could try removing the o2 sensor from the side not throwing the code and swapping o2 sensors and seeing if the code follows the swap 

 

Depending on the year and engine on this, it might not be possible. I know my 2001.5 3.5L has unique sensors for each bank, so the same sensor can’t be used on the upstreams and downstreams, without changing the wiring. Mostly because wire lengths are different, and so are the connectors, but I don’t know about all pathfinder models being that way. I know it was a huge pain to source the correct O2 sensor for my Bank 2 Upstream sensor because there were like 8 different styles.

 

It’ll be cheaper to change the O2 sensor, and easier, of course. Here’s the thing, the cats typically don’t degrade as fast as the sensors unless you’re having engine problems, like rich conditions or misfires. Its a lot more rare for the cats to go, but not unlikely. I would suggest changing the O2 sensor first, and running a bottle of Cataclean (or whatever it’s called. Just follow the bottle directions. The stuff works really well). Worst that can happen at that point is you have a new oxygen sensor, and that’s peace of mind if you have to change the cat.

 

I’ve got almost 200,000 miles on my pathy, with stock cats. Still passes emissions like new, and that engine’s been through some rough times.

 

IF you’re really wanting to crack down on it before spending the money, pull off the cat and shine a light through it. See how well you can see through it. If its breaking up, or very dirty, it might be worth changing. If it’s dirty, but not breaking up, it might be possible to save.

Once it’s off, and looks to be in one piece, grab a bucket and about 1/4 a cup of laundry detergent, and fill up the bucket with water and the soap. Let it foam up, and soak the catalytic converter in it for 12+ hours. When you take it out, give it a good rinse, and allow it to dry. If you have any high-temp rust-protectant paint laying around, it doesn’t hurt to clean up the outside and give it a coat, but it’s not necessary.

 

If it looks much cleaner inside, throw it on, bolt everything up, and see how it does. I also don’t recommend doing the lacquer thinner trick if you read up on that anywhere. It can cause some issues with the fuel pump on these vehicles.

 

Good luck!

[cham]

Ive been having issues with a recent drop in mpg. Used to be getting around 230-250 per 16 gallons and have recently noticed a pretty significant drop. Haven’t been able to go through full tanks yet but it seems I’m barely getting 100 miles for half the tank. I will say I live in the city and do drive a lot in it but thats mostly to get in and out of it. Now it seemed to have started happening after I replaced my fan clutch due to excess noise which obviously cannot be the problem but I also used some cataclean around the same time. Can this stuff have adverse effects? Ive also noticed some louder than normal pops coming from the exhaust after parking the car which makes me think something broke off. Any experience with this? And I hate to ask but what is our cats setup? Do we have 4 and the 2 closest to the engine are called precats? Ive heard a lot of terms thrown around in other threads but cant quite find the correlation yet. Sorry for all of the questions, thanks.


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[Sjackson2]

cataclean could cause some issues. its a solvent. you could have broken loose some carbon deposits that could be clogging up your cats. exhaust popping and poor gas mileage definitely point to this. What year is your vehicle? Technically they are supposed to have two pre cats and two resonators. But.....california models and some other(mine for instance) have 4 cates. The resonators on mine are also catalytic convertors 

[cham]

I have an 2002 LE. It shouldn’t be a cali spec vehicle as the PO was from the north east, only one owner previously. Is there potential for some pretty nasty damage to the engine if I let this go on? I’ve heard of the timing of the valves allowing a split second of opening for broken bits to be sucked back into the engine from back pressure destroying the cylinder walls. Also if I had clogged cats wouldn’t I be getting a noticeable amount of increase in the temp gauge when climbing up a hill or putting some sort of strain on the vehicle because all of the exhaust gets backed up?


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[Sjackson2]

running with clogged convertors is not a great thing...and yes if they break apart pieces can possibly be sucked back in. As far as the engine getting hotter...not necessarily. Especially now while its cold out. You could remove the pipes from behind the precats and inspect them and see how they look 

[cham]

That sounds like a good idea, how am I to know whether my exhaust has 4 cats or 2 pre-cats and 2 resonators?  Correct me if I'm wrong but they look very similar.  Also if there are broken bits of ceramic floating around in there does this generally mean I'll need to replace the whole system or at least try to clean out the internals of the rest of the exhaust?

[Sjackson2]

Look inside of them. If the two little resonators before the muffler have the little honeycomb stuff in them they’re cats.  And if there’s broken bits they either need replaced...or you can punch out the rest of them and use spark plug non foulers so you don’t throw codes 

[Sjackson2]

But you can keep the rest of the exhaust if it’s not all rusted out. Just replace the cats 

[spicyheckboi]

Look inside of them. If the two little resonators before the muffler have the little honeycomb stuff in them they’re cats.  And if there’s broken bits they either need replaced...or you can punch out the rest of them and use spark plug non foulers so you don’t throw codes 

Would you use those non foulers on the o2s before and after the cat you punch out or only the downstream one? Is that going to affect its running as well?

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[Mr_Reverse]

In my experience, P420 and/or P430 have been failing cats. If there are other codes, I would resolve them first, but if no other codes, it has been the cats going bad. If you have an IR thermometer (non-contact type) the simple check for the catalyst health is to get the engine up to operating temp. Hold engine speed at 2000-2500 rpm for a minute. Let engine go back to idle and measure the temperature at both ends of the cat. A healthy catalyst will be at a minimum of 150°f hotter at the outlet than the inlet. If the temperature is nearly the same at both ends, the catalyst is worn out and not functioning properly anymore. If it is hotter on the inlet than the outlet, you have a restriction and the cat is bad. 

 

The upstream cats are the primary cats and the ones the ECU monitors for function. The downstream cats are reduction cats that are primarily for reduction of NOx. There are a few states that have California type emissions requirements, so finding California emissions across the country is quite common. 

 

Don't know anything about cataclean, but I am naturally suspicious of things like that being much more than snake oil. Catalyst failure used to be an uncommon problem. Used to see 1 or 2 per year, now I see a couple per month on average. Problem started getting noticable a couple years after E10 fuel became mandated across the country. The ethanol is not a good idea for our gasoline engines and does cause more than just corrosion issues in older cars and trucks. My 93 Pathfinder ECU is not programed for it. What it sees is a lean condition at the exhaust, so tends to richen the air/fuel mix to get the correct reading from it's O2 sensor. That causes fuel economy to go down and makes the catalyst work harder and hotter. Not good things in the real world. 

With the VQ engines, you have 2 O2 sensors that are after the cat, but the upstream sensors are actually fuel/air sensors. Similar to O2 sensors, but have a much wider measuring range and much more sensitive. Easy way to tell the difference is an O2 sensor will have up to 4 wires. An AF sensor will have 6.