ok heres the code i got when i got my engine scanned: PO421.

The guy there said its my cat not warming up quick enough because im not using a high enough octane gas. but for a while i was using premium and it was still there quite often but would go off every once in a blue moon.

Now heres what the ticket says:

The PCM has determined that the warm up catalyst efficiency for bank 1 is below threshold for the current engine operatin condition. (Bank 1 identifies the location of cylinder #1, while bank 2 identifies the cylinders on the opposite bank)

Code:PO421

Definition: Catalyst efficiency low-bank 1

Explanation: The oxygen sensors monitor the catalytic converters ability to store oxygen.

Probable Causes:
1. Catalytic Converter defective (Failure possibly due to #2, 3, 4)
2. Engine misfire or running condition.
3. Large vacuum leak
4. Engine oil leakage into exhaust- vavle guide seals, piston rings.

My dad is suggesting to just buy a new o2 sensor and c what happens. if i do that should i just go and buy an air/fuel gauge so i can see how my engine is running.

Or should i just go and buy a new "honeycomb" as the tech. put it which would cost like 300 or so bux. then he advised to just go to a muffler shop and get them to put on a universal one that would just be like 100 or so bux.

N e suggestions would be very much appriciated. Thank you. ;)

lol ok i just saw another thread with this same problem and so now im going to go get the new front cat. lol. :laughing:

repost.

and its under recall.

I had the same error code on my Lexus. I have 170K miles on mine. Just took it to the dealer yesterday. Right exhaust manifold is cracked, which they said is most likely causing the reading. My Lexus oxygen sensor is bad too. Total bill for manifold & O2 sensor with labor is about $1,500. My manifold crack is bad enough that you can hear a "puffing" sound in the engine when it starts. Good luck with yours.

tx u to ;)

Basically this means that the oxygen sensor downstream of the catalytic converter on bank 1 is detecting that the converter is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system. You will likely not notice any drivability problems, although there may be other symptoms. The code may be more likely to occur after the engine has had numerous cold starts in the past 1-2 days. This code P0421 may mean that your catalytic converter is no longer functioning properly, an oxygen sensor is not reading (functioning) properly or a sparkplug is fouled up.

The simplest thing to do when this happened is to reset the code and see if it comes back. Next step is to measure the voltage at the oxygen sensor on Bank 1 (the rear sensor, or the sensor after the converter). The voltage should be low and steady (~200mV, depends on the vehicle). If the voltage varies (e.g. 100mV to 600mV) then it's time to replace the catalytic converter. In fact, it would be a good idea to test each oxygen O2 sensor while you're at it. One thing to note is that many vehicle manufacturers offer a longer warranty on emissions-related parts. So if you have a newer car but it's out of it's bumper-to-bumper warranty, there still may be warranty on this type of problem. Many manufacturers give a five year, unlimited mileage warranty on these items. It's worth checking into. Good luck!!!

cripes, does no one read around here?

its UNDER RECALL. the cat. converter is dead. New software will prevent it from happening again.
the end.

thanks! I got this code today, set up an appointment to see the dealer Saturday afternoon!

As again, this code means a umbrella of things. Best is to narrow down with other symptoms. Mine had this (CEL on) and would jerk when accerlerating ( changing gears) or when AC second fan kicks in. Both these mean extra power for the car.

P0421 was fixed with coil plug change. Based on the OBD II reading it would say which cylinder misfires. By looking at the manual or speaking to mechanic figure out which of the coilplugs need to be changed.

no, there is no "umbrella" of things to fix this.
the cat efficiency code is nearly 100 percent correct when it appears.
A misfire will not cause a P0421. However, a misfire can ruin a catalyst. A misfire will introduce a p0300-P0304 code.
An inoperative O2 sensor will not cause a P0421, as it needs a functional O2 to perform a catalyst test.

no, im afraid that P0421 is amazingly accurate, and as Ive said 3 times now its UNDER RECALL. Incorrect software causes the cat to overheat when run excessively at W.O.T., thus ruining it.
the software update should be done for free, and it extends cat. converter replacement to 100k.

Manybrews I am aware and respect the years you work as a mechanic but your communication skills and tact suck. I have tried to work with you on other issues I had with my Endeavor and have read your other replies in different forums. Now I am visiting texas and have an issue that if you would have responded with more information other than Recall it's over I may have obtained greater knowledge. In many cases our vehicles are over 100K and are no longer warrantied by Mitsubishi as is my case with my mother's Lancer. Had you utilized the time that you took to say nothing except it's under recall over and over and described the parts and part numbers for replacement and a little summary on repairing techniques maybe you would put your knowledge and advice to better use. And seeing that you defend Mitsubishi with all of your might I would appreciate you answer this.

In my mother's case her 2002 Mitsubishi Lancer ES, which has been maintained as required by the owners manual had the PCM upgrade done to the vehicle at 80k (she never recieved a letter and has lived at the same address since she purchased the car brand new) and all of a sudden now at 100k her upper cat is shot (in my opinion from having ran 80k on the old PCM settings) and now Mitsubishi says "the car is over 100k it's not our problem" and won't even meet me half way, in my opinion that is lack of responsibility on Mitsubishi's part. Because you are inside the system and can take care of your problems yourself having been a mechanic it's easy to defend the company but when you are on the other end (customer) and deal with crappy service advisors, crappy mitsubishi customer service reps, and get charged a ridiculous amount for the work being done, and get short answers like the ones you provide with your reply's it's not hard to understand why most of us are frustrated beyond belief with this company. I love Mitsubishi cars, I think they are comfortable, for the most part reliable, and fun sporty cars, but Mitsubishi's followup and customer care sucks, they had no problem taking my money and getting me in but they have a serious problem following up on their products.

Lastly, I am very much in love with the New Lancer particularly the Ralliart, but unfortunatly all my Mitsubishi's are very much upside down and I put alot of money down and have a low interest rate and they are in excellent conditions so for one I am stuck with what I have and second because of the attitude that you and the rest of Mitsubishi exhibit when talking to Mtisu owners of new or old vehicles I don't foresee ever buying another Mitsubishi product again.

im not here to make friends. I offer answers to questions. If people don't like the way I answer, they could merely take it upon themselves to do some studying and investigation about their cars and cars' problems. My word, they could even call someone! or howabout this... actually PAY someone to diagnose and repair it!
you seem a bit too intelligent to NOT realize that getting answers on the internet will almost surely be wrong 80 percent of the time.
I also get sick of people asking the same questions over and over again, without doing so much as a "search".



I'm not 100 percent sure I believe the "never got a letter" part, as most of the time the recalls aren't performed its due to someone seeing a letter with "mitsubishi" on it, and merely tossed it in the trash believing it to be an advertisement.
regardless of that, think about what you're asking. Catalytic converters have a finite life. They DO wear out. The previous software may have altered its life, and maybe not. But as much as you may like every problem to be taken care of for you in regards to automobile repairs and maintenance, thats just not too likely too happen when a car has over 100,000 miles on it.
Like it or not, cars over 100k have wear, no matter the manufacturer. I have NEVER, EVER gotten into a car from any car builder on the planet with over 100k and not easily found 1000 dollars worth of damaged, worn, or neglected parts.
lastly, I am not immune to the almighty dollar. Just because I get a break in that I save labor, I certainly dont save much on parts. Everyone here gets some type of benefit from whatever their career choice is, whether its being an auto tech, a pizza maker, a dentist, etc. Too say I dont have to deal with poor customer service is pretty silly.


you make it sound like this website is in someway affiliated with mitsubishi.
Obviously, its not. I certainly dont have to come here and offer advice to anyone, but I like cars and feel I can help in some cases. HOWEVER, when I see people that are too lazy to read, need to have their hands "held" constantly, and blame everyone but themselves for issues that were created by said person, I get a little nuts.

Do you have any idea what its like to work in an industry that EVERYONE feels is somehow "trying to screw you"? Its a real pain in the ****. People seem to think that all mechanics do is change oil and plug in a magic computer to repair their cars, then charge gobs of money.
Frankly, I wish that was the case, because then my job would be a lot easier. However, I need to deal with people that are basically insane.
You wanna hear some stories? Like the lady that brought in her montero because it was making a noise, but when she got there she wanted us to ride with her dog due to the fact that only HE could hear the noise? Yep, apparently the dog barked at the floor when he was in the car, so it must have something wrong.

then of course there's the person that left a pound of raw chicken in her car under the seat, but was screaming at us because "my new car stinks so bad its making me sick!".

Howabout the 3000gt that mitsubishi VOLUNTARILY bought back after 3 attempted repairs to its hood. The woman said that in the hood of her red 3000, she could see the devil. Yep. Even after mitsu painted the hood, etc.etc. They just decided that this lunatic was not worth dealing with any longer.

this list is endless, but all true. So before you tell me how I dont understand having poor service, you need to see my side, which is the side wherein EVERY customer comes in with a shitty attitude, a chip on their shoulder, and the belief they're gonna get "screwed".

Manybrews, I will agree with you on customers being A*** and it seems to be the attitude many take in all service type of business's. Unfortunatley with my service issues with many dealers particularly Mitsubishi are not the mechanics but more so on the front end with "service advisers". I believe that most mechanics are quite competent and in fact I will many times sneak around to the garage and get usefull, honest, and informative information from the techs or mechanics. And trust me I have seen with my own eyes some of the idiotic complaints other customers bring while I am have waited for service or ordered parts. With regards to my issue on your comments I just feel that you have valuable information and honestly if I was in your area I would take my car to you, I have paid thousands of dollars throughout my years of vehicle ownership for work that I can't perform myself, and unfortunatley due to economic circumstances like college, health, and the economy we simply cannot go out right now and pay what mechanics such as you rightfully deserve as compensation. All of us work in various types of industries and see what we believe as stupidity and ignorance but we need to be able to sit back and understand that not everyone has the same competencies. With regards to my particular situation with Mitsubishi, I am a nurse, if today I gave a patient a prescription or made an error of any sort and the issue did not have ramifications until 6 months or 1 year later I am still responsible for that decision, and the hospital for whom and I work for and myself must take responsibility. I feel this to apply to any service or product given. In the case of the car, I know cats don't last forever a vehicle does not last forever, but I find it to coincidental that the exact parts and symptoms discussed in the TSB have failed on a vehicle that has been matained per spec requirements and 20k after the PCM was updated all of the symptoms and failures as perscribed by Mitsubishi Motors have happened. I believe Mitsubishi should have at least worked with me on the matter given the facts describe before. As I described above I believe you have great knowledge on the subject matter but I think you should not blanket all individuals as the stupid customers you have had to deal with and instead help and educate people, and you are correct you don't have to give any advice since you are not getting paid but on the same token it's not necessary to repeat short answers in a manner the belittle's people.

the good news about the failing cat is that it will not affect performance or drivability at all.


so unless you have a local emission testing law that prohibits licensing, you only have to deal with the "check engine" light being on.