A couple of years ago my check engine light went on and diagnostic tests indicated an oxygen sensor had failed. I replaced it for $150 and the next day the light came on again...all the while the car is running fine. I ignored it and drove around for about a year before having the car diagnosed again with a sensor problem...this time #2! I replace that..light goes out and comes on the next day again. This time I took the car back and had another test which came out that #3 oxygen sensor was gone! I am starting to think nothing was wrong in the first place and the car is programmed to kick out these readings according to the mileage! Anyone else have this difficulty?

 

02 sensors are probably the #1 'good sensor' replacement or part/s change.. Not always, but being that they are monitoring exhaust content/Cat efficiency anything upstream can possibly cause or set an 02 code.. Like an intake manifold o-ring leak (I'd look there as a possible fault), exhaust leaks, PCV, vacuum/intake line bleeds, EGR, EVAP, MAF Sensor/contamination, IAC and so on..

They don't kick out codes due to adate or mileage, and they do fail, but usually not at a high frequency like two in a few days.. The 02's generate a low voltage signal (typically .75-.999v +/-) for the PCM as an input that 'ranges' up and down (depending on the exhaust content/throttle angle/load)or whats called 'cross counts'.. Higher voltage generated indicates for rich exhaust condition, and low voltage generated/indicated signals for lean conditions.. If the 02's don't cross count consistently,, or stays low voltage say from a intake leak for too long,or even rich, the PCM will see the indication and set the CEL light and code..