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P0431 - 2001 Mazda Milenia w/o supercharger

alj262alj262 Posts: 1
edited July 2014 in Mazda
The issue I am having is:

originally my car failed emissions with a few of codes....P0400:EGR Flow, P0421:Warm Up Catalyst Efficiebcy Below Threshold(Bank 1), P0431:Warm Up Catalyst Efficiebcy Below Threshold(Bank 2).

I fixed them, by cleaning the egr valve, and clearing the ports just behind/inside of the throttle body. then car ran/runs great....this morning(3/22/10) I was going to finally take the car in to "pass" the emissions test and the check engine light came back on....I went to AutoZone and they checked the code for me now a P0431 comes up again...any tips would be greatly appreciated!! there doesn't seem to be an exhaust leak and I hope the catalytic convertor isn't bad.


  • kaisdadkaisdad Posts: 2
    edited April 2010
    almost the same exact thing happened to me today with my 2002 2.5L. i had P0431 + P0400; i cleared the P0400 by cleaning my EGR Valve and i thought i was home free until i was a 1/2 mile away from the emissions spot and the CEL came on. so instead i went to autozone and the P0431 code is the only code.

    i'm going to take it up to meineke for an exhaust test to make sure the cat conv is good. also, my o2 sensors have never been replaced (i'm at 102K miles) and they are recommended to be replaced every 100K. so hopefully the cat conv is good and after doing some research replacing the rear left hand O2 sensor may clear the code (see this). i'll let you know how it goes. BTW, found these DRIVE MODES to ready the system monitors once you do your fixes >>
  • kaisdadkaisdad Posts: 2
    edited April 2010
    I took it to Meineke and the Cat Converters are good; and also know that the exhaust test is FREE. So I replaced one of the O2 sensors that is in the front of the car close to the radiator. You'll see one at the top of the and one at the bottom. Swap out the bottom one. For me it was easiest when I hoisted the car up on a couple of jack stands and pulled off the guard under the body that is almost directly below the sensor. By the way, You can save a lot of money by going with a Bosch universal O2 sensor.
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