O2 oxygen sensor. Is it still required?
 

They have discontinued emissions testing here in Ontario. So does one still need the O2 sensors?
when i hook up odb scanner, it shows a "?" , against o2 sensor, but no codes and everything is fine. I was just wondering if the sensors are week and worn? I did not want to replace 4 sensors as expensive.
2006 Sebring 2.7L, 6cyl. 182,000 km
What do you suggest?
Thank you

When the computer doesn't have good data to operate with, it makes certain assumptions and then guesses at certain settings. The guesses are not as accurate as can be when operating on good feedback data. The car will run better and use less gas when everything is operating as designed. Will you get sufficiently better gas mileage and performance to justify the expense of new O2 sensors? Who knows? but probably not. Your call.

O2 sensors are still necessary for control of the air/fuel ratio for the most efficient engine operation (i.e. may run like crap). Besides the pcm expects the sensors to be present and will set a dtc and light the check engine lamp. No need to preemptively replace an O2 sensor; only need to replace if it throws a code. It is also likely it is illegal to remove emission equipment (it is in the US)

If the law supports their removal, you could have a muffler shop delete the cats, and the sensors after them... keep the front sensors. The sensors before the cats are capable of providing the engine with all the necessary information it needs. The rear-most sensors mainly just measure how well the cats are working.