I was at the dealership last night and asked about what weight oil they put in the TCH. Turns out they use the correct weight. I mentioned some of the experiences that people on this board have had and he incredulously said, "it states 0W-20 and 5W-20 right on the oil cap.

He also said that a customer came in with a Prius with the check hybrid system light on. They finally figured out that he had gone to a Jiffy Lube and they threw in the standard weight oil. Once they switched to the recommended grade the problem went away.