The Full Form of I3S is‍ Idle Stop Start System.

Idle Stop-start systems (also called “Idle Stop”) that automatically shut the engine off when the vehicle stops moving to save fuel, and then automatically restarts the engine when the driver presses down on the accelerator pedal are becoming more and more common on late model vehicles. For city driving, Stop-Start systems can improve average fuel economy from 8 to 15 percent or more! The actual savings will vary depending on the drive cycle and how much of that time is spent idling or not moving.

Stop-Start technology has been around for nearly a decade on hybrid vehicles such as the Toyota Prius. In fact, Stop-Start technology is one of the features of all hybrid vehicles. This includes “full hybrid” vehicles like the Prius and Ford Escape hybrid that can use their high voltage battery and electric motor to drive the vehicle in electric mode only under certain conditions, and “mild hybrid” vehicles that only use their high voltage battery for automatic engine Stop-Start and to boost engine performance when accelerating.

Some examples of the latter approach include the Honda Insight, Accord and Civic hybrids, Saturn VUE hybrid, Saturn Aura Green Line, Chevy Malibu ECO hybrid, Chevy Tahoe and GMC Yukon hybrids, and the 2013 Buick LaCrosse with eAssist.

Idle Stop-Start is not required by law. But as time goes on, more and more auto makers are incorporating this feature into new models to improve their overall Corporate Average Fuel Economy (CAFE) numbers. The goal is to raise CAFE standards nationwide to 52.5 mpg by 2025.

The Idling Stop System automatically switches the engine off at traffic lights and other brief stops, eliminating wasteful fuel consumption. When the Idling Stop System is switched on, it automatically turns the engine off and on for you when you stop and start up.