Ok well here goes, this is a strange one I might admit although it might have been addressed at another time, I can't use the search to find help. 95 SE Maxima, check engine light came on about a year ago, it was the knock sensor and 02 sensor codes. We replaced one of the 02 sensors and the codes went away for a few months and then popped back up again, this time it was one of the other 02 sensors, replaced it and it went away. A week later the CEL came back again with the same codes, moral of the story, the CEL won't go away and we've replaced all the 02 sensors (some more than once) and the knock sensor. And now the car won't pass emissions due to something with the 02 sensor. Anyone have any ideas?

 

Defective o2 sensor or your engine is running so poorly that the o2 readings are way off tripping the min/max voltage values set to trigger the cel.

 

Have you changed all 3?

One code with almost always trigger the other so before you change the third O2 sensor, check the knock sensors resistance with an ohm meter

 

All three sensors have been changed and so has the knock sensor. I don't think the engine is running poorly, because it performs just like our 97 SE and it isn't having any problems at all.