How OnStar Works

You've probably seen or heard the advertisements for OnStar—the General Motors communication system that alerts emergency services if you've broken down or had an accident. Not only that, it can unlock your vehicle's doors, provide, real-time driving navigation and even deliver stock market price updates (we're not kidding here). But who among us can explain how it works? How does that reassuring voice know your vehicle's airbags have inflated and you need help? We'll give you the easy version.

Telematics
OnStar is defined as a telematics service, a combination of telecommunication and informatics that provides data to a mobile source, much like your cell phone or PDA. To better understand how it works in relation to other hard-to-figure-out products and services, the system incorporates elements of GPS, cellular technology and onboard electronics.


GM introduced the system in 1996 as a user-friendly safety tool. A push of the button on a panel in the rearview mirror connects the driver with an OnStar advisor using fairly conventional, hands-free cellular technology and the vehicle's audio system. The GPS technology gives the advisor your exact location (by calculating the amount of time it takes for a radio signal to get from satellites to the vehicle's position), which can be relayed to the appropriate emergency service. If the vehicle is in an accident and/or the airbags deploy, the advisor contacts you then alerts emergency services. If injuries are serious, this advance alert can save lives.


The accident alert is relayed to the advisor from OnStar's Advanced Automatic Crash Notification System (AACN), which includes a component equivalent to an airplane's "black box," known as either an Event Data Recorder (EDR) or Crash Data Recorder (CDR) and part of the Sensing Diagnostic Module. Other elements of the system are front and side sensors, a cellular antenna in the vehicle's roof and the Vehicle Comm and Interface Module (VCIM) that transmits signals to OnStar's cellular network. It all sounds very NASA-esque.


This next part gets even trickier, though. As you're tooling down the road, the black box collects data, seatbelt use, throttle position, braking action, etc., every five seconds. The unit records and relays that data when the g-forces in the vehicle fall into the 1 to 2 range. When the airbags deploy, the system is on full alert and records additional information. This data is retrievable for about 45 days (or 250 ignition cycles) after it is recorded. Auto engineers use the EDR or CDR to analyze the cause of the accident and to make safer vehicles. It also helps reduce product liability risks for the manufacturer.