This may answer why lower milage in winter, note the temp is taken off the oil temp sensor to determine engine run time. O2 sensor has a heater built in so has not much of a cold weather effect like normal cars do.


extended drives, especially in winter: HSD cars such as the Prius do not shut off the gasoline engine until the oil temperature reaches a set point. Brief drives do not allow the engine to warm up, burning extra fuel per mile traveled .