oxy sensor 96 caravan..poor milege

Ive been told that an oxy sensor either works or it does not.nothing in between.in other words ive been told that if no codes are up and the van is running fine then the oxy sensor is not the reason the van is hard on fuel.can someone shed some light on this topic.should i change the oxy sensors to try and improve milege.has anyone done this and gotten better milege.

Oxy sensors don't have to throw a code to cause poor mileage. As they age they tend to cause the vehicle to use more fuel but are not bad enough to send a code to the computer. Replace the sensor and you should see a change in the mileage. You can also make sure the plugs and wires are in good shape so that the engine will burn fuel at top efficiency. Just a couple of suggestions.

My O2 sensors were operating JUST "within range". Fuel mileage suddenly went from 20 to SEVEN mpg!! Changed the O-sensors and it came back.