Rep Power: 0

I just replaced my front O2 sensor about a week ago and since then I've seen a 3 MPG improvement. I was unable to get the rear sensor loose but I had my mechanic do that for me today. I've got 133,000 miles in my 2002 Civic EX. Just wondering if I should change the rear one since I just replaced the front one. Will I see any further benefits?

 
Rep Power: 256

no dont bother unless the check engine light comes on and throws the code for a malfunctioning secondary o2 sensor.

 
Rep Power: 0

okay if thats the case...my engine lean some light came on to replace the O2 sensor...i just erased it and its been almost 5 months and it didnt turn on again...

whats that ?

 
Rep Power: 812

primary sensor affects gas mpg and engine performance, secondary (in the cat) is just to tell the ecu youre not polluting the air. most sensors are rated 100k miles, mine only lasted 80k. if engine light comes on, it time to change em. even if you turned off the light, it will come back again later. it was probably a code for 02 sensor "slow response" which means its just getting old and cant take readings fast enough.

 
Rep Power: 0

Thanks everyone! Good to know. That'll save me an extra $50. On a completely unrelated note yesterday I just changed my oil and started putting Lube Control LC20 in. I can already tell that my engine runs smoother. Might have to pick up some FP Plus as well.