My check engine light won't stay off more than a couple days, and keeps sending the code that the O2 sensor is problematic. Its been reset 3 times and keeps coming back on. My mechanic tested the O2 sensor (I think it was the front) and it tested fine, so he saw no need to replace it. Gas mileage has been as good as always. So I'm running around with the check engine light unless my gas mileage, power, or driveability show problems. Anyone got a clue to what the problem might be? This started about the time I had a both a leak in the crank case (which was fixed and cleaned up) and the starter went and was replaced. I've had a CAI for about 3 years and never had a problem with the o2 sensor, and its is at least 50k miles old, and probably original at 108k. Thanks.