How to test and when to replace Oxygen Sensors?

[ksa8907]

So I have noticed that the fuel trims in my CTS are doing funny things. I have been watching the injector pulse width as well as fuel trims and it looks like the passenger side of the engine is using 5-10% more fuel than the drivers side.

Now this could be blamed on the timing chain as it has stretched over time, but I think it might be the O2 sensors. Does anybody have some experience with this or just want to give me a good excuse to buy new ones?

Thanks

[user removed]

How much does a replacement cost? Can you swap them without a lot of work then confirm the issue has moved to the opposite side?

In the old days they would get "lazy" before tripping a code.

regards
mech

[oil pan 4]

I know a guy that went to vehicle instrumentation school and says to change the O2 sensor every 50,000 to 80,000 miles.
He says its because the sensor gets lazy as it gets older, he also lives in eastern Virginia.

[ksa8907]

Replacements are $65 a piece, seems to be reasonably easy to get at so I may try to swap them around and see if there is a difference. I also read where a guy had good ones reading roughly 7 ohms and a bad one at 11 ohms, so I'll make sure to test them when I get them out. 5% less fuel would be over 1 mpg gain.