The CEL on our 2004 vibe was on, per the codes and a mechanic said it was the O2 sensor upstream. I replaced the O2 sensor with an Amazon purchase - forget the brand off hand. The previous owner said he replaced it also about 6 months prior to our purchasing it. I did note that the one I removed looked different - it only had one row of holes, whereas the one I put in had about 4 rows of holes (not sure if that makes a difference). The plug was the same, the overall length of the sensor that goes into the exhaust was the same length, just the number of sampling holes was different. Of course
the previous owner could have replaced it with the incorrect sensor. How many sampling rows should the upstream sensor have?
I replaced it, if it was the problem, should the CEL go off right away? Ours did not so I cleared all the codes, and so far the CEL has stayed off, although I haven't rechecked lately to see if all the sensors are reporting in yet - it's been close to 100 miles so I'm hoping for the best at this point.
Thanks