Question about 2004 Mitsubishi Endeavor

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SERVICE ENGINE SOON LIGHT CAME ON READS CODE P0431 AND P0421

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  • Anonymous Mar 23, 2014

    Hello not solved still problem Ok explained you everything began had problem het gasket was repaired but also has problem of the outlet that is in the canine to connect to charge the cell that towards which do not operate light Board doors is not blocked don't walk remote control course light of service this on but was then set service engine are and there gave me those code p0421 and p0431 No it is a result of the electrical problem

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Converter is not working as efficiently in Bank 1 and Bank 2 (two codes)...

P0421 - Warm Up Catalyst Efficiency Below Threshold (Bank 1)
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.

Symptoms: You will likely not notice any drivability problems, although there may be symptoms. The code may be more likely to occur after the engine has had numerous cold starts in the past 1-2 days.

Causes: A code P0421 may mean that one or more of the following has happened:
The catalytic converter is no longer functioning properly
An oxygen sensor is not reading (functioning) properly
A sparkplug is fouled up

Possible Solutions:
Measure the voltage at the oxygen sensor on Bank 1 (the rear sensor, or the sensor after the 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.

P0431 - Warm Up Catalyst Efficiency Below Threshold (Bank 2)
Basically this means that the oxygen sensor downstream of the catalytic converter on bank 2 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.

Symptoms: You will likely not notice any drivability problems, although there may be symptoms such as a rough/hard idle when cold.

Causes: A code P0431 may mean that one or more of the following has happened:
The catalytic converter is no longer functioning properly
An oxygen sensor is not reading (functioning) properly
There is an exhaust leak

Possible Solutions:
Inspect for exhaust leaks. Next step is to measure the voltage at the oxygen sensor on Bank 2. 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.


Hope this helps.

Posted on May 05, 2011

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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.

Check the O2 sensors and catalytic convertor.

Posted on May 05, 2011

  • 2 more comments 
  • Andrew
    Andrew May 05, 2011

    Sorry, it is both banks due to the presence of the two codes. They mean the same thing but refer to Bank 1 and Bank 2 respectively.

  • O2Sensor Aug 30, 2011

    meinverstand canyouexplain exactly what downstream means. I have a Mit Montero limited 2001 edition with a P0431 code. To buy an oxygen sensor for this car you are being asked if it is Bank2 driver's side before aor after the cat. Or Bank 1 passengers side before or after the cat. Please qhich one is this P0431 code. Thanks

  • Andrew
    Andrew Aug 30, 2011

    @O2Sensor I'm not sure where it would be located off hand but the auto parts store should be able to tell you whether it is located before or after on your car.

  • ajnjg2007
    ajnjg2007 Feb 24, 2013

    What do i need to buy so that my montero sport does not have the p0421 code anymore? I just bought this car Do i need a whole new catilytic convertor?

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Code P0421- Call Mitsu before you do anything! I called my nearest dealership today and for those who dont know, if your check engine light is on and its showing fault code P0421 this may be from a factory recall on the warm-up converter and a PCM reflash. MILEAGE OF THE CAR DOES NOT EFFECT THIS RECALL. Anyone whos had problem with a dealership not doing the repairs because of mileage needs to contact another dealer or the owner of the dealership. This is what the service manager told me today so though I'd share. Getting mine fixed tomorrow at 10am, I cant wait.

For more information about this code Google "Fault Code P0421" You'll get tons of information Last edited by Swankzer; Jun 2, 2008 at 12:31 PM.

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Hi,

So you have a P0421.

A code P0421 may mean that one or more of the following has happened:
  • The catalytic converter is no longer functioning properly
  • An oxygen sensor is not reading (functioning) properly
  • A sparkplug is fouled up

As far as running conditions if it performs normally, you most likely need a catalytic converter. The good part of this is there shouldn't be any abnormal running conditions, so it should be fine unless the engine is running very rich for some reason. (it will usually smell badly when this happens) However, on rare occasions the cat can get hot and melt down causing an exhaust restriction..bad gas mileage, low power, and possible fire potential, but most likely this is not the case. (this is generally speaking here and covering all the bases... )

The most common thing with P0421 that the fuel injection computer detects that the cat is not performing to federal specs an need to be replaced. You will need to have it fixed before your vehicle inspection.
Good luck and I hoped this helped you.

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