I have a 95 Max with 79,000 miles. About 500 miles ago my check engine light came on. The code translated to the rear O2 sensor. I reset the light and waited figuring it would come back soon. About two weeks ago it came back, so I figured it was the O2 sensor again and was planning on troubleshooting and/or replacing the sensor this weekend, but never checked the code or reset the light. Well today, I drove my car somewhere and the engine light was still on. The car sat for about an hour, and when I started it up again the check engine light went out. Puzzled, I turned the car off and made sure the light came on with the key in the on/run position, which it did. Is this normal for the light to go out after a period of time? I'm sure my O2 sensor still needs some attention, but what gives with the check engine light?

Matt