02 sensor went out after 3 months
 

Any idea on this happens ? I just replaced them 3 months ago and the rear 02 sensor went out again. 2 years ago I had them replaced at Toyota, this doesn't seem normal any ideas?

List non-stock exhaust bits, ecu tune, work performed in that interval. Still will be guesswork, but at least a bit less baseless.

Headers is all I have on the car,I did open flash my car about a month ago thank you for the response

Just that most cases i recall reading problems with damaged O2 sensors on this forum, were during improper / careless header installation, as they are rather brittle/easy to damage and such, hence the question. Though i wonder if that might be applicable for repeatedly O2 sensor failure cases.
Hard to guess, what else may affect already installed ones though, but as they are mounted in exhaust header, i mentioned those things in that post, as near and what somewhat may affect O2 sensors. Misinstallation of sensors during of header being one, second - maybe damaged wiring by heat (not touching hot headers by chance?), maybe bad wiring harness socket electrical contact, reseat?, tune .. i recall that custom ecu tune for bangs/pops that throws unburnt fuel in exhaust, can damage catalisators .. maybe sensors aswell? Well .. all just wild guesses, but at very least i'd check wiring if one of cases of failure were after longer time of it working properly after being bolted in and not mechanically touched since.