Should O2 sensors be changed if no DTCs are set indicating an issue? I assumed they are working properly if no codes are present.

Thanks!

 

If they have 100k miles on them it would be a good idea. Mine had about 190K on them when I changed them, picked up a few mpg when I did it too.

 

If you've got 100K miles or more, they're costing you money in fuel mileage! If you wait for the check engine light to come on, you might have been able to pay for one of them with what was wasted in fuel!

 

Blazin and Captain,

Thanks for the information. Both precat ones have been replaced in the last 50,000 miles/two years but both were throwing codes when I changed them. I guess if no codes are thrown ,the old sensor is within range, but further from the target, hence MPG not optimized?

Blazin, I assume you changed yours with no codes present and your mileage increased?

Slightly off topic.. my 95 Corvette OBDI threw H44 (Bank 1 lean) and I searched days trying to find a vacuum or exhaust leak to no avail. This reading made the car run rich. MPG dropped 25%. Black smoke was abundant at WOT. I then swapped the sensors and then got H64 lean bank 2 (the lean followed the sensor) swapped them back and got H44. I then disconnected the sensor and naturally got H13 Bank 1 O2 circuit fault; however, the rich condition stopped and MPG went back up to near normal even with the car running in open loop. I plan to get a replacement sensor for it shortly although the car appears to run fine and MPG is normal with the disconnected sensor. I guess I'll go ahead and replace both sensors as they've never been replaced with 254,000 miles. Hwy MPG is about the same as when new (26-27).

 

Yes mine had no codes present, but you could watch then on the torque app and when compared to a new Denso unit the new sensor would sweep 3 times for one that the old stocker did. They were just LAZY.