Helping Overcome Trauma for Children Alone in Rear Seats Act of 2017 or the HOT CARS Act of 2017 This bill directs the Department of Transportation (DOT) to issue a final rule requiring all new passenger motor vehicles weighing less than 10,000 pounds gross vehicle weight to be equipped with a system to alert the operator to check rear designated seating positions after the vehicle engine is turned off. The alert shall: (1) include a distinct auditory and visual alert, which may be combined with a haptic alert (i.e., vibrations); and (2) be activated when the vehicle engine is turned off. DOT must enter into an agreement with an independent third-party for a study on retrofitting existing passenger motor vehicles with technology to address the problem of children left in rear seats after the vehicle engine is turned off.