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P0421 what do you think of this
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pvlover
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PostPosted: Mon Apr 27, 2009 3:03 pm    Post subject: Re: P0421 what do you think of this Reply with quote

^^

It's basically fooling the O2 into a fake reading.
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thm73
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PostPosted: Wed Jun 03, 2009 10:24 pm    Post subject: Re: P0421 what do you think of this Reply with quote

Ya know - when I went to do this 'fix' for my P0431 code, I found my front post cat o2 sensor was quite loose. I've decided to tighten that well, and see if that takes care of it. It would sort of explain the tendency for the code to appear with big pot holes, and when it rains.
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thm73
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PostPosted: Thu Jun 04, 2009 11:16 am    Post subject: Re: P0421 what do you think of this Reply with quote

Ya - tightening the o2 didn't do it. I have the P0431 - is that the O2 that is way back behind the transmission on the drivers side?
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steve12955
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PostPosted: Thu Jun 04, 2009 6:46 pm    Post subject: Re: P0421 what do you think of this Reply with quote

Hello,

I believe P0431 refers to the downstream O2 sensor (below / after the catalytic converter) on Bank 2 which is on the radiator side (not the firewall side which is Bank 1).

Good luck,

Steve
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MPVHubby
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PostPosted: Wed Mar 24, 2010 7:26 pm    Post subject: Re: P0421 what do you think of this Reply with quote

With 155K mi on my 2000 MPV-DX and a persistent P0421 code I installed this mod on the firewall side pre-cat sensor after disconnecting the battery cable to reset the ECU and have driven 350 mi with no return of the CEL. One more happy no-fouler customer!
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steve12955
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PostPosted: Thu Mar 25, 2010 7:54 am    Post subject: Re: P0421 what do you think of this Reply with quote

Hello,

If the codes reappear, try switching the non-foulers to the O2 sensors AFTER the catalytic converters; that is, the downstream sensors. Originally, I also thought they should go on the upstream sensors but I was corrected here and on other sites.

They've been installed for 15 months and about 10K miles and my '00 now has about 185K miles and the original converters in place and it just passed another emissions inspection.

Good luck,

Steve
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12Ounce
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PostPosted: Thu Mar 25, 2010 9:22 am    Post subject: Re: P0421 what do you think of this Reply with quote

Rufus wrote:
.....What do these things actually do to make the code go away??....


Some folks think this method is somehow cheating the sensor because the sensor is "no longer in the exhaust stream". Huh? The sensor is still only sampling exhaust ... nothing else.

You will notice the sensors have a rather massive body .... why?... heat dissipation perhaps? My theory: the defoulers add more metal (and distance away from the exhaust ) allowing the sensors to work in a friendlier enviroment.

??
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Jonathan Landrum
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PostPosted: Tue Oct 05, 2010 10:27 pm    Post subject: Re: P0421 what do you think of this Reply with quote

This workaround seems to have worked for me as well.

However, collateral damage from a rookie mistake when hooking the battery back up: wedding ring got caught and shorted leaving a ring of another sort around my finger. I've never had that happen before. It could have been much worse.

2001 MPV V6, 214k
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Dan-jan
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Joined: 04 Feb 2009
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Location: Grand Junction, CO

PostPosted: Sat Feb 12, 2011 2:01 pm    Post subject: Re: P0421 what do you think of this Reply with quote

Another happy customer with this repair, at least so far. We've been having a P0421 every other month or so, and last week when we got another one I decided that I needed to try this idea.

I bought the 42009 non-foulers, as they are the washer-style which the O2 sensor is (see photo).

It took me about an hour to do. I was concerned about two things: that my O2 sensor might be hard to get off, and that the wire might break from the twisting of removal. I didn't plan to disconnect the sensor.

The sensor came off easily, and I was careful to distribute the wire twisting upstream from the sensor, rather than overstress the wires where they come out of the sensor. Seemed to work ok doing that, and I pre-twisted the wires again upon assembly so that when the sensor was tight the wires would be neutral - untwisted. One of the trickier things was re-securring the wire afterwards, due to the new position of the sensor. I used a couple of zip-ties which will hopefully last a good while. I also took off the 4-bolt frame member/skid plate thingy for easier access.

Did a test drive, and all seems ok! See other photo for completed installation. Hopefully, no more P0421.

2003 MPV LX - 235k miles
1951 Willys CJ3A





IMG_8201_s.jpg

IMG_8201_s.jpg - File downloaded or viewed 9283 time(s)


IMG_8207_s.jpg

IMG_8207_s.jpg - File downloaded or viewed 10076 time(s)

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tiobita
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PostPosted: Thu Apr 21, 2011 8:14 pm    Post subject: Re: P0421 what do you think of this Reply with quote

Just another happy customer, been driving for almost 600 miles and no code so far. I had a P0421 code every 40-52 miles. Then began searching, found this thread and decided give it a shot. I used four (4) 42009 non foulers because my car uses two (2) downstream O2 sensors. My car is a Mitsubishi Galant 2006 ES.

Thank you guys for posting this. Very Happy Smile Wink

Best wishes,
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sergiovv
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PostPosted: Wed May 11, 2011 10:52 pm    Post subject: Re: P0421 what do you think of this Reply with quote

Dan-jan wrote:
Another happy customer with this repair, at least so far. We've been having a P0421 every other month or so, and last week when we got another one I decided that I needed to try this idea.

I bought the 42009 non-foulers, as they are the washer-style which the O2 sensor is (see photo).

It took me about an hour to do. I was concerned about two things: that my O2 sensor might be hard to get off, and that the wire might break from the twisting of removal. I didn't plan to disconnect the sensor.

The sensor came off easily, and I was careful to distribute the wire twisting upstream from the sensor, rather than overstress the wires where they come out of the sensor. Seemed to work ok doing that, and I pre-twisted the wires again upon assembly so that when the sensor was tight the wires would be neutral - untwisted. One of the trickier things was re-securring the wire afterwards, due to the new position of the sensor. I used a couple of zip-ties which will hopefully last a good while. I also took off the 4-bolt frame member/skid plate thingy for easier access.

Did a test drive, and all seems ok! See other photo for completed installation. Hopefully, no more P0421.



THANKS for the info , i am thinking on do this but i dont know where this sensor is located , is underneath the driver ??by the tire ??, is it hard to remove....?? please just a little help.
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sergiovv
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PostPosted: Mon May 16, 2011 3:10 pm    Post subject: Re: P0421 what do you think of this Reply with quote

Ok here is my story , my Mazda MPV 2003 had 3 codes P0174, P0306 and P0421 so reading here and there specially at this forum find out that replacing the PCV hose may get rid off this codes and went to the MAZDA Agency and get it for $90 ....back at home while i was trying to replace it i noticed that the AIR INTAKE HOSE had a huge hole ..so i decide to replace that one first instead of the PCV hose and also was cheper $40....after that went to get the inspection done and they said i had one code not ready and it was the P0421 .
(warm up catalyst system (RH) efficiency below threshold)

guess what .?? yeah the non-foulers really worked .!! i went to autozone and got them . i did exactly what Dan-jan said .

hope this help to other people , before they get ripped off.. 2 days before do the non-foulers fix i went to a shop that had a big sign..( WE ARE CHECK ENGINE LIGH SPECIALISTS) thought they may know some tricks ...but all they did was check codes with the OBD-II device and tell me what needs to be replaced so in my case was the 4 catalyst converters that was going to be $1000 .....

so replacing Air intake hose removed P0174 and P0306.
and the non foulers fixed the P0421.
thats the nicer inspection sticker i ever seen in my van.
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tryba1
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PostPosted: Mon Oct 10, 2011 6:19 am    Post subject: Re: P0421 what do you think of this Reply with quote

I did this on Bank2, (P0431) and have drove 200 miles with no CEL.
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rollie1960
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PostPosted: Mon Jan 16, 2012 8:48 am    Post subject: Re: P0421 what do you think of this Reply with quote

thm73 wrote:
Ya - tightening the o2 didn't do it. I have the P0431 - is that the O2 that is way back behind the transmission on the drivers side?


Ours does the same thing I just make sure I make sure it doesn't rain when taking it in to get the emission test here in Texas oh another thing I do is I take it to our local auto parts just to make sure nothing is stored in the computer.

Our 2001 MPV has been doing good with this trick for years we LOVE our MPV sure would be nice if Mazda were to bring the MPV to the U.S of A. Im also bringing this thread back so new members can read it.
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rollie1960
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PostPosted: Mon Jan 16, 2012 8:48 am    Post subject: Re: P0421 what do you think of this Reply with quote

thm73 wrote:
Ya - tightening the o2 didn't do it. I have the P0431 - is that the O2 that is way back behind the transmission on the drivers side?


Ours does the same thing I just make sure I make sure it doesn't rain when taking it in to get the emission test here in Texas oh another thing I do is I take it to our local auto parts just to make sure nothing is stored in the computer.

Our 2001 MPV has been doing good with this trick for years we LOVE our MPV sure would be nice if Mazda were to bring the MPV to the U.S of A. Im also bringing this thread back so new members can read it.
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