Question about 2000 Mazda Protege

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1999 Mazda Protege ES/1.8L Manual Trans

Have code P0420.replaced both o2 sensors,still have same code.This is the only code showing.Cleared mil light and went through another drive cycle and still have the same on both sensors are equal as far as the data displayed /lean with exact numeric reading.I bought the car used and someone had taken out the center muffler section and had installed one of those darn loud mufflers on the rear.I got rid of that but haven't replaced the center section as of yet.light came on two weeks after i bought it at 105,000 miles,I could reset the light and get it inspected but now it has 222,000 and when i reset the light the cat monitor and evap monitor does not reset until the light comes back on,therefore it won't pass emmissions and can't get it inspected witout monitors on.Is it possibly the cat is too far gone and needs replaced?The car still runs great with no problems no rough idle,once in awhile it will hesitate during take off from a stopped position then is fine after that.

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Cat is probably gone if it is the stock one, but i also know the mass air flow sensor could be the problem, and its also the cheaper of the two things you could do (MAS or pre-cat). you can try cleaning it with the spray stuff they sell at any local auto store. readings online say this car running rich will kill the catalizer in two weeks so you might want to keep that in mind.

Posted on Sep 20, 2008


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Posted on Jan 02, 2017

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SOURCE: p0420

There should be 2 O2 sensors. One is located before the catalytic converter and one downstream from the converter. I believe they should be right where the catalytic converter is.

I hope this helps! :) Let me know if you need any further assistance in this matter.

Posted on Feb 20, 2010

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SOURCE: mil bulb not work .conector

P0420 = catalyst system efficiency below threshold (bank 1).

P0401 = Exhaust gas recirculation-insufficient flow detected

P0740 = Torque converter clutch, circuit malfunction.

Posted on Mar 07, 2011

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