Turns out bad O2 sensor (the one adjacent to radiator). Replaced under warranty. Another seven months go by, now at 23,800 miles. Check Engine light again...same problem.
Question is: What the heck. Toyota dealer gives some mumbo jumbo about having consulted with Toyota Techline and they are "aware of some Problems" and are working on it. Toyota Techline supposedly sez that there appears to be a bad batch of senors....Hard to believe. Mine car was built in July 03 in Japan. The replacement was installed in March
04 in the USA. Seems that "batch" would be long gone.....I don't want to be replacing this part every seven months. Any specific suggestions on what I might ask Toyota to do. I have to take the car back next week sometime when they "get the new sensor in."