I have a '96 Ford Contour with a 4cyl. I have had 0171 (bank 1 lean) codes in the past and replaced the O2 sensors to fix it. I am now on my third set as of last week at only 140k. The problem is that the 0171 code came back within a couple days.
So I hooked up my Elmscan to see what the readings would look like, never having watched the sensors before. The downstream sensor is flat, exactly what it should be. The upstream sensor varies rapidly. This is normal from what I have read on this site. The voltages, however are weird. I read that the voltage should vary from .1 volt (lean) to 1 volt (rich). I watched negative .3 or so up to several volts. I don't recall the exact number.
Can a sensor give that kind or range, even if bad? The sensors I bought were the cheapest I could find. So today I bought the best I could find, but I don't want to put it in quite yet. Could something else be going on?
Thanks for your thoughts.