Replace O2 sensor or Not replace O2 sensor

Our 97 3.3l Grand Voyager has 117000 mi and I'm preparing to give it a tune up. Plugs, wires, belt, ect. I was curious whether the the O2 sensors should be replaced at this time or I should wait until a obvious problem(check engine light, poor mileage or driveabililty issues) arises. I have read on other vehicles, once the check engine comes on, the catalytic converter is fried.
Thanks!

The question is what is your gas mileage. Did you pass your emissions test? I wouldn't change the O2 sensor unless I had a reason. No, I don't agree once the "check engine" light is on your catalytic converter is fried. The CC is supposed to last the life of the car if you use correct gas.

At 117K you're close to replacement time on those O2's. It's not true that when the light comes on you're cat is fried. It's only fried if the check engine lights starts BLINKING and you keep driving on it like that. Life of an O2 sensor is around 100K. That start to get lazy after that and it does affect your gas mileage in small ways.Just replace the upstream sensors, no the post cat sensor. If you want to read an in-depth article on O2 sensors, go here: http://free-auto-repair-advice.blogspot.com/2007/07/understanding-oxygen-sensorswhat-they.html

Another article in favor of replacing the 02 sensors: http://www.obdii.com/articles/Replacing_Oxygen_Sensors_Preventive_Maintenance.ht ml

Don't know that I would go with the Bosch recommeded interval at the bottom but, I think at 100K plus it's not a bad idea. Don't use the less expensive types you have to splice the connector on. These sensors are sensitive. If it's not spliced exactly right it could give you problems sooner or later.

Yes, the gas mileage is questionable, but I don't drive it daily, my wife does, and she forgets to push the trip button at the gas station. I live in a state with no mandatory inspections,(you should see some of the 'fine' automotive equiptment on our roads!) so we don't have emisson testing. I glad you mentioned which sensor to replace, I would have thought they needed to go as a pair.

100,000 sounds reasonable on the upstream sensor. I have 113,00 on my '96 3.3 and the gas mileage has not changed. I know I am close to replacement and need to do it soon.

LAZY