I have just replaced an almost new oxygen sensor on my 2000 Grand Am. After about 40 miles, the check engine light came back on again. I have not had a chance to check it, but I assume it is the oxygen sensor again. What am I missing?
The problem is most likely not the actual sensor, but that the sensor is reading the gasses going by, and they're not reporting what the computer thinks it should see.
It needs to be diagnosed, so don't throw any more parts at it. Read the code, or get it read, and post it back.