P0431 obd2 error code
 

How difficult is it to remove and replace the driver side catalytic converter?
Would welding in a generic replacement catalyst be worth the hassle?
(2001 montero sport)

I am in same predicament. My 2001 Monty XLS CEL comes on, and P0431 is on my OBDII reader. I put Pass4Sure in the tank, and right after 60 miles, the darn CEL came on... right before I was going to take it to CA emissions test. All I really want to do is get the light to turn off for about a week/hundred miles and take it to emissions so it will pass. CA emissions, since she is 2000 or newer, only has to be inspected and have the computer read. They don't hook it up to the dyno.

How can I get it to turn off for just a week - long enough to get her inspected? I don't really want to pay 1400 dollars for a new Cat, only to have the CEL come on three months later with some other issue.

I saw a post about seafoam in the oil and PCV. Not sure what he was referring to, since he had sport model. Does anyone know about that? Surely it would not hurt to try. And when you guys do that, do you reset your codes, or remove the battery to do so. Can they tell you reset your codes at the smog inspection place?

Having a montero in california is not a nice thing when it comes to catalyst problems or codes. No replacement cats available that is CARB certified. So only oe from dealers will do, a bit expensive because it's the complete y-pipe that has two cats. I think you can install aftermarket CARB certified cats like the ones from walker or magnaflow. You'll have to buy two them and have a shop install it,but considering parts and labor and that it won't last as long as oe cats...maybe the oe cats are your best option not unless you have no plans of keeping the montero for a few more years.

It has been a fairly descent car. I bought it new in Virginia and moved to CA four years ago. It's reliable. Drip a little oil in my garage, but still in good shape. I don't know what CARB certified is. I took it to a muffler shop yesterday and they said 1200 dollars for the non-oem, weld in cats. They said if I bought the oem one, they would install it for 300 dollars. The gal said I might replace the 02 sensors to see if that makes the issue go away, but from this thread, I think that is bad advice since they are almost 200 dollars each.
What do you think of this part? What would be wrong with installing this in CA? https://www.mitsubishipartsonsale.co...MtNWwtdjYtZ2Fz

Contact the dealer and ask if it is california legal just to be sure. If it aint, I don't think shops would install it since it would be illegal to install them. It seems they have same part numbers for california and non california cats,could they be the same? If you click on the parts on online parts stores they show same items,tried this on two online parts stores.

I emailed the seller yesterday and got a reply this morning,they were asking for my VIN to verify if the cats are california certified. We'll see if they reply within the day.

I ordered mine and had it installed by local muffler shop. I had sprayed two sensors with stuff to get them out so it would be easier for them. The third I did not know existed. CEL went off, but week later came back on with code indicating the sensor I didn't know about. I bought one on ebay for ~20 bucks and had them install it. CEL off for several months now. All is well.

Do not waste your money by replacing the Oxygen sensors. The fact that the computer is showing the P0431 code indicates that all O2 sensors are working as they are suppose to and you have an issue with the catalytic converter. Unfortunately cat converters do wear out. It happens on all vehicles eventually. OEM is the only source I've seen that provides the "drop in" replacement of the entire Y-pipe with left and right bank cat converters. The aftermarket weld-in is an option, but I did not hear much of good things about them. It seems like Montero PCM is very nit-picky and do not play well with aftermarket (continue to throw codes). Get an OEM replacement and have a peace of mind for many years. It is possible that Montero cats are 50-state certified and therefore will be OK for California use. If you can't install them in California, drive out to Nevada or Oregon and have a shop there throw them in while you chill out at the poker table :)