i have 2001 QX4 with 130k miles.
its pulling code 420.
my garage is telling me it needs a new Catalytic Converter ($900+) on one side. i read somewhere that you can replace the the 02 sensor or "reflash the ecm' to sometimes make this problem go away but he tells me this is an 'internet myth'. every time he sees code 420 it is the cat converter.

i looked in the FSM but I dont see any information on how to replace this? is this something I can do myself? does any one know if I have the bolt on or the welded type? if its a bolt on ... can that simply be cut out a new one 'welded in place'?

years ago my wife's mazda needed a cat. the garage wanted $1000+, I took it to a small 'barrio' garage and the guy cut out the old one with a sawzall and welded in a new one for $200! he did all that in about 20 minutes.

also, a stupid question.... - is the FSM supposed to give exact step by step directions for replacing / repairing stuff or are mechanics supposed to know from experience how to do stuff? for example, i thought about replacing my own alternator but I couldnt find any instructions on how exactly to remove the old one (there is a lot of stuff in the way!)

I'm not a mechanic so I can't answer that, but I learn mostly from this website. I've been on here forever and someone usually posts about stuff. I agree about the alternator. I just did mine two weeks ago and I also have an 01 QX4 with almost the same mileage. I decided to give it a try and it was a beast. But I replaced it for $150 alternator from auto zone and didn't have to pay a shop $500 to do it. It wasn't technically hard, but just getting access to the bolts and everything was a nightmare. It's literally like 2 connections and a couple of bolts, but where they are you just can't get leverage on anything. It probably took me about 6 to 8 hours and a lot of cussing and breaks to chill out from not being able to get screws started etc., eventually you just get lucky and get it started and it's a lot of just slow wrench turning. Anyway, good luck with the cat, never had to do that.

Josh

If you are lucky the code will clear on its own. I've had two catalytic converter related codes appear on my 2001 Pathfinder, now at 190k, but each time they disappeared in a week or so. They were a couple of years apart.

I had P0430 and P0420 when I bought mine and new cats fixed it right up. It's only six nuts attaching it to the exhaust header and 2 or 3 bolts to the exhaust pipe (no welds), but they were rusted over enough to make it...challenging. I attempted to do it myself but most of the nuts on the header were impossible to get to; they're pressed up against the firewall. I ended up giving up and having a shop do it, and I'm still satisfied with my decision. I bought a pair of Walker cats at $200 a pop and installation was about $500 (maybe less) so if you buy your own you could probably get the one done for half what you were quoted.

Walker 16343
Walker 16344

If you're interested in doing it yourself, crawl underneath and have a look. For other repairs, I'd recommend getting the Chilton book. It's been pretty invaluable to me. The only downside is it sometimes downplays how difficult a repair is and may not have critical tips. That's what sites like this are for!

I've heard of putting spacers on the downstream oxygen sensors to get rid of the code. That will pull the sensor out of the stream of exhaust so it won't be able to sense as well. There's a thread here somewhere on doing that, though it's likely not legal.

Some food for thought: cats generally don't just go bad. The usual cause of death is the engine running rich. The extra fuel breaks down the cat and it will start performing below threshold, which is what the code is telling you. Since only one side on yours is bad, that hints at leaky or clogged injectors on one bank. Pay attention to and address things like hard starts, rough idle, smoke out of the exhaust, etc. or you could end up paying for the same repair in the future. In my case the biggest culprit was the fuel pressure regulator and fuel damper were leaking copious amounts of fuel out of the vacuum line and into the intake manifold. I'd recommend you pull the vacuum hoses off them and start the engine. If gas starts dripping out after a few minutes, you'll want to replace those as well.

Good luck and let us know how you fare!

thanks guys for the tips. I will let you know what I do about the CATs

If it turns out you have to replace your CC then you can minimize cost by buying it yourself from Rockauto.com and then taking it to a independent muffler/exhaust shop for the installation. You didn't say what state you live in but for California compliant Cats the best price I found was $280/each. A reasonable price for installation would be about $150 each side. Per Atraude's advice I would also make sure there is no current issue with excess fuel being dumped into the exhaust. Usually when one goes bad the other is not far behind.

thanks for the response.
yes, unfortunately , i do live in california and i notice online that every store selling cat's seem to say not available to ship to california... i will check rockauto.com as you suggested
1. do you think i have to buy exact fit bolt on replacement or can i have old one cut out and a new 'generic one' welded in place. a did a quick look see underneath and i see lots of corrosion on those bolts
2. come to think of it.. the last couple years, the car does seem to put out a lot of 'rich' exhaust on start up than i recall in the past. I have very limited understanding of fuel injection system (I do have the FSM). if i pull off those vacuum lines, where am i supposed to be looking to see if fuel is dripping out?

When you pull the vacuum lines off the FPR and fuel damper, you'll be looking for fuel coming out of their vacuum port. What happens is there is a small diaphragm in each of them that expands or contracts depending on the vacuum, allowing more or less fuel to pass inside. These membranes can crack over time and allow fuel to leak past and into the vacuum lines. If it's a particularly bad leak, you'll find fuel leaking out of that vacuum port while the engine (and fuel pump) are running. This video is a good example of what it looks like when that happens.

Rich exhaust while the engine is cold is completely expected. The computer intentionally runs the engine rich when it's cold in order to get it warmed up as quickly as possible, which is called open loop. When it detects that it's warmed up, it uses data from things like the oxygen sensors to determine the ideal fuel/air blend (closed loop). As an example, when the engine coolant sensor (which is separate from your temperature gauge) goes bad, the system never enters closed loop mode and it runs overly rich all the time.

California has crazy tight regulations around catalytic converters (what can be installed, where, how and when) which is why I think most companies simply opt to not sell to Californians (too much effort and liability, I'm guessing). Sorry, I don't have any specific advice on that front. Maybe hit up a shop or two that does exhaust exclusively and get a quote from them?

thanks Atraudes. I just spent some time understanding a bit what the vacuum lines purpose is.
i will check it out on my car.
I have a 2001 and i have a cheapo obd2 code reader. the thing only shows basic info (codes and p/f for a few montitors. do you know if my car is new enough to show info like closed/open loop and sense if coolant sensor is working? in other words, if i buy a new obd2 will i see a lot more information or did 2001's not have all the fancy sensor feedback capabilities

also - i understand the basics of how the car monitors if the cat(s) are bad. it is comparing the pre and post o2 sensor outputs... is it possible if i have a fuel problem (caused by the vacuum issues you mentioned or by a bad coolant sensor) can that be confusing the 02 sensors and thus making it look like a bad cat convertor? or... if i followed your earlier post correctly, are you saying that having all that extra fuel probably destroyed the cat convertor in the first place and i will have to replace the cat as well as the vacuum related components? im hoping to avoid the cat expense

wrt california crazy regs... If i can find a way to purchase a 48 state cat, will it even work on my car without trrowing the code again? in other words does California want some special convertor even thought the basic mechanics and sensors work the same way.... from a practical perpsecitve.. what happens if you buy a car in texas and then move to california? obviously your car doesnt start throwing different codes when you drive over the border but maybe when they stick that sniffer in the tail pipe , you dont pass ? just wondering...
thx!

As far as OBD readers, a lot of people here have had great luck with Torque on their phone and a bluetooth OBD adapter. I tried that but couldn't get it to actually read any info on my car, so I can't personally speak to this approach. I ended up buying a Bosch OBD reader which works well enough, though a computer or phone-based app would probably be preferable due to ease of use. That said, I'm not positive if either will tell you if it's in open or closed loop mode though I'm guessing they do. Regardless, you can get all sorts of advanced info like fuel trims and start looking at what's out of whack compared to what the FSM shows as in range.

I would think if the O2 sensor was detecting excess fuel it would throw a code specific to that, or simply lean out the mixture in which case you'd have driveability and/or idle issues. In my case it was definitely the cat because as soon as they were replaced the codes went away and haven't come back since.

Based on the info in this Q&A, it looks like there's two categories of cars made for each model produced: those that are manufactured to meet CA emission standards that are to be sold in CA, and those that meet federal standards which are to be sold everywhere else. CA emissions cars will only accept CA cats. Federal emissions cars will accept either. So based on that, it sounds like CA emissions cars have different parameters burned into the ECU as far as what to look for in the downstream O2 sensors, and federal-only cats won't perform to that level. If you bring a federal emissions car into CA and get it smogged they'll see that it wasn't manufactured to CA standards and hold it to those standards instead of CA standards.

I do know that when you bring a car into the States from out of the country you're held responsible for bringing it to federal standards before you can register it.

you are right about the 'grey market' car being your responsbility to bring it to country standards. I ran into that many years ago when i moved to Europe for a few years. I had wanted to bring my 300zx there because they sold for 300% more than here! but when i looked into it I would have to get all kinds of stupid stuff installed to pass their red tape (one thing was electric motors to tilt the headlights up/down.

i just crawled under my car to get a look at the cat's but now im getting confused if im even looking at the correct part!!! the FSM shows the TWC (3 way cat) on page FE9 (it labled part #11) . this part is easily accessible and have 2 bolts in the rear and 3 bolts in the front. is this really the CAT? i can see an O2 sensor 'on the front end of this part' but it is called "rear O2" sensor. I thought the o2 sensors are on each side of the CAT. if you follow what im saying.. this would mean that the CAT is actually in front of this part im looking at (ie closer to the engine and much less accessible from under neath the car.

update: i just searched the whole FSM and i do find in EM-11 that is shows a TWC "Manifold' part where the front o2 sensor is located. why would the 2 sensors be on each side of a manifold rather than on each side of the actual CAT? am i missing the big picture here.
thx

It is kinda odd that the exhaust diagram doesn't show the cats or exhaust manifolds! The cats that are the cause of your codes are on EM-11, part 3. There are upstream O2 sensors on the exhaust manifold right before the cats, and sensors right behind them (downstream) which are mounted on those TWCs you saw in the FE diagram.

I'm having a hard time producing a diagram or picture. Hopefully someone else has one handy.

i just tried to cut / paste pictures from teh FSM into this post but i dont think this forum allows it.
anyway I do see the picture you are talking about.
to summarize ... there are 2 different components 1. a TWC convertor manifold (which sits closest to the engine) 2. TWC (which connects downstream of #1

sounds like you are saying i have to replace #1 which will not be at all easy to get to ... if #1 is the actual cat then what the heck is part #2?

thx

It's the blue parts here you're looking for



Looking at the diagram, you may want/need to replace the washer and mesh washer at the same time.

thanks for confirming the part. yeah... i thought it was too good ot be true that the cat converter was the 'other part' that is more excessible downstream of the part in blue. Infinity FSM is a bit misleading by labeling that other part TWC (three way converter). the cat convertor seems extremely difficult to get to so i will not attempt to change it myself. also , based on the shape and fit of the parts it doesnt look like i can have a shop 'mcguiver' a weld on generic cat convertor since there are no 'tubes' on either end of this thing.

I did take your advice and checked for fuel leaks in the 2 parts that have vacuum lines attached. happy to say that mine were dry.

btw - i also tried to insert a picture into my post but couldnt do it. how did you do it... im guessing I need to have some certain posting rights to do it?

Nope, no special privileges needed Basically you upload it to something like imgur (my preference since they never expire photos), grab the URL of the actual picture, and wrap it in the img tags. Hit the quote button on my post with the picture and you'll see what I mean.

ugh... its 2016... storage is cheap...suprised they make you link to a 3rd party server

by the way... i thought is cool how you colored in the component with blue. how did you do that ? did you edit the pdf file of the page of the manual?

Yeah I get that it probably limits liability and simplifies things on the server, but it does become an additional hurtle for new users.

Once I saved the picture I opened it in Gimp and used the fill tool to fill the white areas with the blue. Discussions are so much easier when you can just refer to the "orange thing" and everyone knows what you're talking about