A Wideband O2 Sensor (and Controller) is a sensor that you install in your exhaust to measure the Air-Fuel Ratio (AFR) of your engine.  Wideband O2 sensors are considered a consumable part that deteriorates during normal use.  We only offer a warranty on Wideband O2 sensors if they fail when first connected as new. If the Wideband O2 sensor has been used then we are not able to warranty it.