aneidiaz

I think maybe all 4 brand new is what properly improves fuel consumption. Maybe not by much, but definitely an improvement slightly. I agree about post cat o2s not doing much. But 2 old and 2 new o2s won't work well together, IMO. If someone is gonna change an o2, they might as well change all of them. Piece of mind at the end of the day you know.

mk2tmr2

iTrader: (1)

If our cars only had two O2 sensors I might be inclined to agree with you. However, we don't. We have four. Replacing all four when only one is known to be bad is quite an expensive endeavor just for peace of mind.

It's not like an O2 sensor is a terribly complex device. It sends voltage between 0v and 1v to the ECU based on oxygen content in the exhaust stream. It's either working or not working. Replacing all four O2 sensors because one goes bad is like replacing all four tires because you got a flat.

aneidiaz

Great point bro. Your absolutely right. I guess I just said that way because I've been recently dealing with this o2 problem. That's what I did. But I had to cuz 2 were shot, and the other 2 were reading terribly low. I changed out everything hoping I won't hear from the exhaust for a few years. Car is currently in the shop cuz a defective B1 S1 o2 I bought. But the other 3 are good. Your right tho bro. I just recommend that to anyone that doesn't mind spending the extra dollars.