Mitsubishi Montero & Montero Sport This sport utility vehicle offers more size than the other Mitsubishi SUVs, but manages to keep a sporty look and comfortable feel, unlike many larger SUVs.

Service Engine Soon light code P0421

  #1  
Old 01-02-2010, 02:59 PM
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Default Service Engine Soon light code P0421

Here we go again. A new year a new freaking problem. We apparently (knock on wood) got the alternator issue fixed and the balancer and pulleys falling off fixed. Now last night the check engine light came on and we started freaking out. We went to autozone and they said some one stole thier coded reader so they couldn't check it. So I bought one for $60 to do it myself.
Ok I got the code P0421 which after some research I see that it's the code for the passenger side Cat. I do not want to spend $500 -$600 more on this truck, it's crazy that after all the money we've already spent trying to make it dependable this last year.
So with all that said, do ya'll think is it okay to drive for a while till we can get rid of it? Maybe a month or two. My wife mainly only drives it to work which is only 2 miles from home. But we do our weekend running around in it. It seems to me it should be okay but I thought someone who's been through this before might have some insight.

Thanks,
 
  #2  
Old 01-02-2010, 04:21 PM
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Yes, unfortunately it is the cat and no, there is no problem whatsoever driving it as is (except for the annoying CEL)

I replaced both my cats after getting P0421 and it's brother P0431. Before the second project I specifically asked the local Mitsu dealer mechanic if it was OK to drive with the inefficient cat and he said it's fine. (I wanted to wait until my truck was due for smog check before spending the $ in case something esle broke in the meantime.) So I drove it for more than 5 months that way with no probs.

Did you reset the CEL with your tester? With both my failures the codes were intermittent and the light would stay off for weeks before reappearing. But over time the frequency shortened until finally I could not reset it.

Ron
 
  #3  
Old 01-02-2010, 04:23 PM
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Won't do any harm, but I recently got a cat for a Chevrolet Avalanche for $70 on RockAuto. Might want to check there before dumping crazy money on one.
 
  #4  
Old 01-02-2010, 08:11 PM
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Yes I did reset it and erased it with the reader. It's a little actron pocket reader. Seems like a good tool to have added to the tool box. I'm glad it was only $60, and not over $100 like some of the ones they had.

Thanks for the insight. We don't have smog tests here so I don't have to worry about that luckily.
 
  #5  
Old 01-02-2010, 08:29 PM
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I have the same tool - one of the best $60 purchases I've made. (It's interesting/fun to take along when shopping for used cars.)

I may have posted this before but one of the fixes I considered before springing for the OEM warm-up cats was an aftermarket replacement. Our local hot rod muffler shop swears he's had good luck with recently avaialble tiny replacemet pre-cats that he also swears he can patch into the very complicated and cramped piping arrangement on our Monty's. He quoted me $375 total for this and I was tempted but in the end decided a few hundred more for the OEM part (plus my own labor) was worth it to be sure the fix would work.

As you probably know, parts alone are in the $700 range and labor is a few hundred more. I got my last (left) cat from www.mitsubishiparts.com for around $530 plus shipping. Replacing is not that difficult. Even if you don't get it fixed this info may be of interest to the buyer. Good luck.

Ron
 
  #6  
Old 01-03-2010, 08:39 AM
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Thats a great idea, I bet the sales person freaks out. Thanks for all the help and I hope it helps someone else too.
 
  #7  
Old 08-10-2011, 06:37 AM
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I am getting code P0421 on my 2000 Montero Sport 3.0 4WD 137k. The other day upon replacing my driver side rear cam seal o-ring. I noticed the wire that comes down to the left of the bracket (02 sensor) was broken. Perhaps, some oil leaked out and melted/broke the wire? I hope it is just the sensor and not the cat.

How many sensors does the MS have? Are both sensors the same? Can someone link me to the correct oxygen sensor? Thanks
 

Last edited by monterodiff; 08-10-2011 at 06:46 AM.
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