The system starts with a report by an OnStar subscriber to law enforcement that their vehicle has been stolen. Once that is done, the subscriber can then call OnStar and request stolen vehicle assistance. OnStar will then use GPS satellites to locate the car and transmit its coordinates to law enforcement. The law enforcement agency can then request that the vehicle be shut down once they have a clear line of sight and know that conditions are safe to do so. The system then reduces the engine speed to idle and slows the vehicle to a crawl, though steering and brakes remain operational.
For many people, just the thought of somebody controlling a button that could stop your car while out on the road is frightening but when you factor in the amount of police chases or stolen cars it could reduce it’s not hard to envisage such a feature becoming standard on all cars in the not too distant future. Additionally, Stolen Vehicle Slowdown portion of the the system can be opted out of at any time with no affect on the remainder of OnStar's services, including stolen vehicle assistance and location. However, GM's research shows more than 95% of owners would appreciate the service.
OnStar has been using its GPS functionality to help locate stolen cars since 1996, and at present handles about 700 such requests each month. The company estimates that since inception, the system has been used to help locate over 38,000 vehicles.