i recently bought a 97 avenger (v6, automatic). shortly after i bought it the check engine light came on. i got it checked out, and the oxygen sensor needed to be cleaned. about 2 weeks later it came back on, and the day i was supposed to take it in to get checked again the light turned off. i decided to get it checked anyway, but there was nothing wrong with it. now a few weeks later the light is back on. it's been on for a few days now. has anyone had a similar problem or know why it might be doing this? in both cases i checked to make sure the gas cap was on tight, and i have no idea what else could be wrong.

 

Mine did the same thing (same year and options). Mine was bank1 upstream (I changed bank1 downstream too). The cel went out after the replacement and came back on a month later, went back to the dealership and they said it was bank1 upstream again. So...I've had the cel on for about 4 years now and I just disregard it. I also get bad gas milage, my advice to you is to get OEM O2 sensor and not Bosche. Also check the bank 1 downstream sensor (the one on the bottom closest to the cat, I also had a valve cover leak (drip) and the sensor wires had oil on it and that may have been shorting the sensor output. I think my precat is/was clogged though, yours might be too.