If the 'fault' that caused the initial code is gone for a certain number of starts, the light will turn off. The code is still held in memory as a history, but with no 'present code' the light will be off.

My wife just reported ours came on...I'll pull the code when I get back into town and then figure out if I need to see the dealer. 9700 miles. Oil service in a week anyway so it can wait....

A