I checked the 02 sensor and I believe it is ok. It checks at around 6 ohms. The car runs fine and is getting normal gas mileage.

I disconnected the battery and re-connected. Afterward the check engine light did not come on and has not since. I accidently disconnected a vacuum line on a valve the is connected to the exhaust manifold several years ago and the check engine light came on. Perhaps this valve is getting old and may be failing.