Do O2 sensors need replaced at some point even if no faults trigger? My V70 has 132K on the odometer and the sensors have not been replaced. My prior S70 didn't even go half this long. Just occurred to ask...
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Steven 04 C70 HPT, 04 V70 2.5T Titanium, 06 S40 2.4i

I had 187K on mine. It depends on how clean the exhaust is. When the front O2 sensor starts to go, your mileage will slowly decrease and give you ample warning.

If you travel 12K/year, and your mileage has gone down 2mpg, a new sensor will pay for itself within one year.

Klaus
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My advice is free, so you got what you paid for...

This does make sense. The mileage has gone down right at 2 mpg. I do keep an eye and figured it was others driving habits until I drove the car solid for a week. I thought the lower mpg might be do to the age of the car even though there is no evidence the engine has grown tired. Should I replace the rear sensor as well or leave it in place?
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Steven 04 C70 HPT, 04 V70 2.5T Titanium, 06 S40 2.4i

The rear O2 sensor lasts longer because it stays cleaner.

Remember to lift each wheel and check your wheel bearings before you spend money.

Klaus
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My advice is free, so you got what you paid for...