2000 Mazda 626, P0420 Question

COASTIE JOHN

MEMBER
2000 MAZDA 626

Greetings,

First time poster. I have a 2000 626 with about 64K miles, a 2.0 and auto trans. I have been working the P0420 problem with mine. I have changed out both the front and rear O2 sensors. Did the rear first. After about 3 weeks the light came back. Did the front, then light came back after 2 months. In the reading I have done, I have seen mentioned that the cat could be bad. I have also seen there is a TSB regarding the limits the PCM senses the tolerence level between the front and rear O2 sensor. This tolerence window is set too close together and sometimes sets off the code. You can take the car into the dealer and they expand the tolerence window within the PCM. I'm not sure if the TSB was for this year 626.

Does anyone have any other ideas for things to check?

Thanks. John

3 Replies

RASMATAZ

MECHANIC
75,992 POSTS

The sniffers are they OEM's try having it reflash

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Monday, April 9th, 2007 AT 7:35 AM

MWHITNEY

MEMBER
63 POSTS

Yes the cat can be bad, abd yes the window in the pcm could be off. You need to get it too the dealer. Cause they are the only one that can reflash pcm. And if the cat is bad any one can replace it but I not sure where this applies to but in NC the law 8 years or 80 k miles free replacement by factory.

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Monday, April 9th, 2007 AT 8:53 AM

COASTIE JOHN