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.

Error Code P0431

  #1  
Old 10-20-2018, 11:21 PM
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Question Error Code P0431

I got an error code P0431 - Warmup catalyst efficiency Low (Bank 2) - for my 2002 Mitsubishi Limited. Suggested replacement parts are the O2 sensors. It seems to me that replacing the sensor is not going to solve the problem, for obvious reasons it has detected an underlying cause for the service engine (dummy) light to go on. Would it be the catalyst are clogged which is why the O2S triggered the dummy light? Thus replacing the catalyst converters rather than the O2S's? Or do both parts need to be replaced simply because the catalysts goes bad so do the O2S's? If so, should all of the O2S's be replaced which one might as well replace the entire exhaust system right?
Can the catalysts be unclogged? If, so how?
 
  #2  
Old 10-21-2018, 11:25 AM
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P0431 means your cats are not working properly,..but it could also be a faulty o2 sensor. Some obd2 scanners can read o2 readings so you can determine If the o2 sensors are working. Sometimes due to age they become slow or die completely. If they are working properly replacing them would still trigger the p0431 code. I also get a P0431 code on my montero once in a while during cold months...i know my cats are on the way out..at150k miles they should be. ��
 

Last edited by carlsson01; 10-21-2018 at 12:36 PM.
  #3  
Old 10-21-2018, 11:59 AM
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P0431 tells computer that your catalytic converter is not working at the efficiency that is required by the emissions standards. Your catalytic converter is not plugged, it simply wore out (loss of efficiency). If you'r experiencing engine stalling, loss of power, etc then look at plugged converter. Plugged converter will not trigger P0431. You'd likely have other codes.

Do not replace O2 sensors. The reason the loss in efficiency of cat converter that WAS detected is exactly because your O2 sensors ARE FUNCTIONING properly. If they did not, you'd get a different error related to the O2 sensors (no communication, open circuit, etc.). You have two possible solutions - 1. replace the Y-pipe exhaust along with the two catalytic converters on them. 2. Cheat... and install spark plug non-foulers over the post-cat converter O2 sensors to "fool" them into thinking that all is well. Your options are limited by where you live in terms of emissions testing for registrations and licensing.
 
  #4  
Old 10-21-2018, 12:45 PM
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Most mechanics would try to change o2 sensors first hoping it would fix the problem...then after a few weeks the same code comes out and you end up changing the cats anyway. I’m really thinking of putting on non-foulers and see if they work,maybe if the p0431 code comes out more frequently I will....
 
  #5  
Old 10-21-2018, 01:45 PM
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Originally Posted by carlsson01 View Post
Most mechanics would try to change o2 sensors first hoping it would fix the problem...then after a few weeks the same code comes out and you end up changing the cats anyway. Iím really thinking of putting on non-foulers and see if they work,maybe if the p0431 code comes out more frequently I will....
You are right about the two-step process for "fixing" cat code. For a mechanic it's a bonus since they get paid twice.
Non-foulers absolutely work. I had to do it on my Monty. Havn't had a cat code for probably several years now.
 
  #6  
Old 10-21-2018, 01:52 PM
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Oh ok hunter...will do the fouler trick for sure..is it obvious from the outside? Some smog technicians take a peek under there..don't know why they do it,never bothered to ask. Maybe to see if I have CARB legal cats on the monty.....
 
  #7  
Old 10-22-2018, 09:15 AM
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It is noticeable if you know what you're looking for. The O2 sensor is basically sitting behind a stack of two extra nuts. Below is the photo of the setup from another vehicle. The rusty colored part with wires is O2 sensor, the new shiny one is the two stacked non-foulers. That's pretty much what it looks like on Monty. Just pointing in different direction.

 
  #8  
Old 10-22-2018, 10:16 AM
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Yaiks...that won’t escape the eye of a smog technician....but like i said,some places don’t bother looking in there.
KMPowell...there’s your cheat to eliminate the P0431 code permanently. I hope you are not from California...
 
  #9  
Old 10-22-2018, 07:03 PM
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Thank you all for your quick answers. So basically the cats need to be replaced which means getting a new exhaust. Is that correct? BTW- I reside in Albuquerque, NM and have 125k miles on the Montero limited.

KMPowell
 
  #10  
Old 10-22-2018, 07:07 PM
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Another question-will running the vehicle with bad cats decline engine performance?
Thank you all in advance for helping me with this issue.

KMPowell
 

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