Ive never replaced one, and wouldnt be able to tell whats a good one compared to a real worn one. If no check engine light is on due to it, how do you know when an O2 Sensor's life is just about shot?

 

recommended replacement is something like every 60k - 100+k. there not supposed to last forever, but some do. the most tell-tale sign is when it runs like ****, seems to run/smell rich, and/or your gas mileage changes. normal mpg is more or less something like 13-14-15 mpg (individual results may vary). if you're getting something a lot worse than that, its worth a shot. only be concerned with the front one (before the cat), as it provides feedback to the pcm for fuel trim. the one after the cat only monitors the cat and you should ignore it unless you get a cel saying your cat is not working.

 

I have always considered relying on the CEL to indicate when the O2 sensor is bad to be unreliable. I believe the O2 sensor can slowly lose its ability to perform all while the PCM thinks it's OK. If the O2 sensor has a lot of white-looking substance on it, or looks burnt black, then change it. I also believe the recommended change interval is 50-65K miles. I just changed out my downstream O2 connector today, and it has 145K miles on it. I bought the truck when it had a little over 120K miles on it and have been performing maintenance repairs as I could afford.

 

Thanks a lot you two! From the looks of it it hasnt been replaced since stock, thats 125k Miles ago. [:@]Will replace it next pay check.