Manager Forum

on a 2002 subaru outback, is the downstream O2 sensor voltage supposed to remain constant if the cat is working properly? We have installed a new cat and O2 sensor and the sensor is fluctuating. 2.2 engine.

welcome to the forum. yes it's suppose to fluctuate. i generally pump gas pedal a few tines to check response time. just a tip on 02's, never use an universal sensor. the connecters used as a splice unless soldered will effect the resistance thus effecting the readings. on rereading the post the sensor reading will fluctuate meaning the output signal. there should be no major change from the base input voltage. a couple of milli volts can be expected but if your getting a voltage drop more than that you have a problem.