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Oxygen Sensors

I recently bought a 2004 Buick Century V-6 engine 3.1 L (automatic transm. w/overdrive). It has 100,000 mi on it & seems to be running fine. My owner’s manual mentions nothing about oxygen sensors. Are they something that should be changed ever so often, or do they only need changing if the car is running poorly & there’s some specific indication that they need changing?

If there’s a problem with the oxygen sensors the Check Engine light will come on and a code will be stored indicating such.


Oxygen sensors don’t need replacing unless the “check engine” light is illuminated and the code indicates an oxygen sensor problem.

If the car is running fine and the check engine light is off, no need to worry about the sensors. Even if one does go bad, it won’t damage anything, and the car will still run until you get it replaced.

As others have already said unless the check engine light comes on and it indicates a problem with the 02 sensor there’s no reason to change it. Most of the time when the upstream sensor goes bad you’ll know it, you’ll have really poor fuel efficiency often losing 25-30% of your normal gas mileage so change it ASAP otherwise you’ll spend more on gas than the sensor replacement will cost you. A bad upstream 02 sensor could cause damage to the catalytic converter, because the ECU will likely be sending excessive fuel to the engine much of which may end up as unburt fuel going into the converter, causing the catalytic converter to overheat, therefore damaging it. My '88 Escort has 518,700 miles on it and I think the 02 sensor has been replaced 2 times since new. The downstream 02 sensor’s only function is to monitor the catalytic converter is doing it’s job correctly, has nothing to do with a/f ratio’s and will not cause damage if left unattended.

Wow, Ford Man, are you going for a million miles on that Escort? Original motor?

Thanks for everyone’s comments…very helpful!


@MIKEMCD77 I plan to drive it until something major happens such as an accident, blown engine or transmission gives out. Most of the normal wear parts are lifetime warranty from Auto Zone and I do my own work so it cost very little to keep it on the road with the exception of gas and insurance. Still got the original motor and never been rebuilt although it’s now using/leaking a quart about every 800-1K miles. The furthest the motor has been into is removing the valve cover to replace the gasket and the oil pan to replace the gasket and clean the oil pump pick up tube.

Back in the eighties, O2 sensors were engine candy and were routinely replaced at 50,000 miles. These days the control systems are much better and so are the O2 sensors. You can usually go a lot farther with them these days.