warm up catalist insufficent in bank 1 P0421

bigdaddy121005 · **Joined:** Thu Feb 26, 2009 7:39 pm **Posts:** 6

I have a 2006 mitsubishi lancer es and i keep getting this trouble code that pops up. I am not sure if it is powertrain or what it is but no one locally can tell me what it even means. Ever time i have it run on a diagnostic tester I get P0421 "Warm up catalist efficency below thresh hold (bank 1)" what does this mean and how can i fix it?

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Jenn · **Joined:** Fri Feb 27, 2009 12:08 am **Posts:** 4

I can SO relate to that. I have an 04 eclipse and have been having the same code pop up for me. I reasearched it some and have a buddy that is ASE certified in 4 different areas and talked to him about it,...

Basically the P0421 code that youre getting is telling you that the O2 sensor BEHIND the catalytic converter is not reading right. Its not powertrain, its emissions.

The first time it happened I was told to get sea foam and run 1/2 can through the top end and 1/2 in the gas tank. That turned it off for about a month...then it came back on.. I replaced BOTH o2 sensors (I dont recommend the universal type), the pcv valve, plugs and plug wires and that was everything that it listed could be the problem except the catalytic converter. No luck with that, so I went yesterday to get a new catalytic converter put on my car and the light came back on 100 miles later. Im confused as to what it is now. the only thing that I can gather from the code is that it means "good luck tryin to fix it" It will not hurt it to be driven with the light on just as long as you arent losing power in the car.

If there is any other way I can help you, just let me know

Jenn

asecmt · **Posted:** Sat Feb 28, 2009 7:34 am

Where were the parts bought from? Only OE converters and o2 sensors seem to work on imports.

bigdaddy121005 · **Joined:** Thu Feb 26, 2009 7:39 pm **Posts:** 6

MY uncles an exhaust man at one of the local shops, so i asked him about the code, he said he will pretty much guarantee that it is the o2 sensor in the exhaust manifold. only down fall is that thing cost between 150 and 250 to buy a replacment.

Webmaster · **Posted:** Sat Feb 28, 2009 11:35 am

bigdaddy121005, you can try replacing the sensor first because it's cheaper but that doesn't mean it will definitely fix the problem. Test that sensor and replace if necessary. If the sensor is fine it's probably time for a new cat.

Also see http://www.obd-codes.com/p0421

bigdaddy121005 · **Joined:** Thu Feb 26, 2009 7:39 pm **Posts:** 6

How would i go about testing the o2 sensor? when it comes to newer rigs i am half blind. get it to bare block and i can do what ever it takes but all the computer relays and sensors throw me off. I actually found a magnaflow cat for less than half the price of my o2 sensor, so i am kind of hoping that would be the issue cause i can't afford a $200 dollar sensor.

Jenn · **Joined:** Fri Feb 27, 2009 12:08 am **Posts:** 4

bigdaddy121005 wrote:

MY uncles an exhaust man at one of the local shops, so i asked him about the code, he said he will pretty much guarantee that it is the o2 sensor in the exhaust manifold. only down fall is that thing cost between 150 and 250 to buy a replacment.

Well, as for me, I went with the Universal cat and o2 sensors....have found out what the muffler shop called the cat that they replaced wasnt a cat cause it was BEHIND the 2nd o2 sensors. so now, Im out that 140 and have to go pay 303 for a direct fit cat, and Ill have to go buy the OE O2 sensors for about 80 a piece.

I called the guy on it and he said that it must have a cat on the manifold.....I wont be going there again....ill find someone that can put the right one on.

bigdaddy121005 · **Joined:** Thu Feb 26, 2009 7:39 pm **Posts:** 6

Probably what they tried to replace was a resination chamber. I know my Lancer has several resonators after the actual cat. But as i said my uncle works in a muffler shop and is well seasoned and actually recomends the magnaflow products.

asecmt · **Posted:** Tue Mar 03, 2009 8:20 pm

Like I said UNIVERSAL parts do NOT work! Don't waste your money. Get a OE converter and a rear O2 and save youself a whole lot of trouble.

Lor · **Joined:** Fri Mar 06, 2009 11:02 am **Posts:** 1

i have the same issue on my '02 lancer this code first popped up after having the cat
replaced(i had another code and was told the cat was bad) so if i move on to the oxygen sensor which should i replace first the one directly into the cat? also how many o2 sensors are on a lancer es?
thanks

bigdaddy121005 · **Joined:** Thu Feb 26, 2009 7:39 pm **Posts:** 6

if it the trouble code says bank one it should be the o2 sensor infront of the cat(at least this is what i have been told).

Webmaster · **Posted:** Sat Mar 07, 2009 11:59 pm

bigdaddy121005 wrote:

if it the trouble code says bank one it should be the o2 sensor infront of the cat(at least this is what i have been told).

No that's sensor #1, not bank #1. Sensor #1 is in front (upstream) of the catalytic converter and sensor #2 is behind (downstream).

Bank 1 vs bank 2 is different - http://www.obd-codes.com/faq/

bigdaddy121005 · **Joined:** Thu Feb 26, 2009 7:39 pm **Posts:** 6

Thanx for the info but strangly as mysteriously as this code come up it has disapeared

ronjoe1 · **Joined:** Fri Jul 24, 2009 9:18 am **Posts:** 1

I there, I'vehad this issue for a little over a year now. It passed inspection last year, but now....no such luck!

It's the sam P0421 code. I've been trying to do alot of research online and found several reasons for the error code. The first thought was an 02 sensor....then I took it to my mechanic, he said it was the catalytic convertor. My question to all of you people (who are far more knowledgable than me) is....How do you know which one it is?

Is it the cat or he o2 sensor...? Either way, they're pretty damned expensive. I found several cats online though for a mere $160...not even sure if thats the right one.

Help would be greatly appreciated!

jpb · **Joined:** Wed Oct 17, 2007 9:29 pm **Posts:** 76

If you read this article it will clear up some of the misunderstandings about catalytic converters.http://www.mail-archive.com/miatapower@ ... 04806.html

warm up catalist insufficent in bank 1 P0421

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