Carpokes

I get random “check engine” signals (could be every few days or 6 weeks) with O2 sensor fault. No evidence of actual O2 fault, and car runs perfectly. Where should I look for the origin of this signal?
BTW, recently installed Ultimate AOS, and signal seems more frequent.

What error code are you getting? If it's an O2 sensor-specific code, my guess would be that one or more of your O2 sensors are getting old and sluggish. The car won't necessarily show any noticeable symptoms (poor mileage maybe), but the ECU can detect when the sensors are not reacting as fast as they should. If your sensors are original or haven't been changed in a long time, probably time to change them anyway. It's best to change them all at the same time. Otherwise, the fast new sensor will make the ECU see the other sensors as sluggish and throw the code again.

Yep, it’s O2 sensor specific. Engine was built 20k miles ago, but I’m guessing the sensors weren’t touched. At 78k mile on the exhaust system, sensors seem like a good bet. I’ll change them to be safe.
Thanks.