what should i do? cat or o2 sensor?


Asked by Mar 05, 2012 at 02:50 PM about the 2001 Mazda Protege MP3

Question type: Maintenance & Repair

i have a check engine light on. here's what happened...  i got the code and it came back "warm up catalyst efficiency below threshold". alright, could be three things... plugs, cat, or o2 sensor/s. well i
have a way of graphing and seeing the voltages on the o2 sensors, so i figured i would start there.
here we go... while warming up, the front o2 sensor goes up and down between .2 and 1 volt. cool,
that's what it's supposed to do, and the rear stays steady near .45 volts. cool, that's what it's
supposed to do. as soon as the engine reaches operating temp tho, the front o2 becomes a little
more crazy and the rear begins to follow the same patter with some variation. shit, that's not right! i
need some advise. then i came here. anyone know what i should do? is this test definitive in the worst
of ways or is there another i can use to be positive?

2 Answers


ITS NOT THE SENSOR AND THE SENSORS DO NOT EVEN TURN ON UNTIL THE CAR IS WARMED UP BY THE WAY so chances are you got cat problems, and if its not affecting your car dont worry about it it wont hurt anything, plugs are always cheap and good to change anyways, so I mean if you really think that its plugs get them, go OEM it will help quite a bit, and hope this helps, but seriously it aint 02 sensors, almost gaurentee it.


that's what i was afraid of. i think i'll just replace the plugs, take out a light bulb and call it good.

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