Check engine Light

[kaktus]

the damn light just turned on today. i was driving and it turned on so i went home and checked the ECU codes. the ECU flashed the front O2 sensor and the knock sensor code. The knock sensor wasn't the problem because i had it like that for 2 years. The real problem is that i just changed the front O2 sensor about 5000 miles ago and now it went wrong? what could be problem? The O2 does not cost much to replace but i just wanna know why did it fail so early. i also notice that there was some oil on the sensor but i found no leak at all.

the car is an s14 ka24de, O2 sensor is Bosch

[480sx]

The o2 sensor could be working fine, but any time you use a non stock sensor theres a chance of you throwing a code. OEM sensors are the way to go, but they are mad expensive.