Oxygen sensors
 

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?

RE: Oxygen sensors
 

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..