MITSUBISHI: Yes, Mitsu offers an Eco mode button. We're told that, when activated, it changes acceleration characteristics, reduces AC control, and if the Mitsubishi is equipped with 4WD it puts the car into 2WD mode. The company doesn't quantify the improvement, simply taking the position, per their representative, "that it's a driving aid to help economical driving."
HONDA: Honda's ECON mode is – as you might expect – a sophisticated answer to a relatively simple question. Here's what Honda reported:
"When the ECON mode is activated, several operating characteristics of the vehicle are modified for enhanced fuel efficiency. The drive-by-wire throttle system provides more gradual response and, to save additional energy, the climate control's fan speeds are lowered incrementally, while other climate control system characteristics are altered based on the conditions. So the climate control will be slightly less aggressive in maintaining a set temperature (this saves energy) and the cruise control will also be slightly less aggressive in maintaining a set speed. Allowing more variation saves energy as well."
Honda won't attribute a percentage improvement because, as they indicate, there are simply too many variables.
KIA: Kia's offers what it calls an Active Eco System in their Soul, Forte and Optima, as well as other 2016 models. As with competitive systems, when engaged it increases efficiency by altering throttle and transmission behavior. If activated, you'll see reduced acceleration, air conditioning and – potentially – a louder engine note.
TOYOTA: All of Toyota's hybrid models have an Eco drive mode button, helping to reduce fuel consumption during trips that involve frequent accelerating. When engaged, the Eco mode will maximize fuel efficiency by changing the throttle input, making that input less sensitive, more smooth. It also institutes a reduction in the HVAC system to reduce its impact on total efficiency.
BMW: BMW supplies a Driving Dynamics Control Switch, allowing the driver to set the ride, handling and drivetrain behavior of the car through a single rocker switch located on the center console near the shift lever.
The four available modes are ECO PRO, Comfort, Sport and Sport +. BMW's ECO PRO supports an "extra-efficient and economy-conscious driving style that can help reduce fuel consumption by an average of up to 20%, with a corresponding increase in driving range." Which begs the question: Why did the owner buy a BMW in the first place?
VOLVO: All Volvo's Drive-E engines have an ECO mode. As reported by one of their product PR executives, fuel economy can improve by as much as 5 %, depending – of course – on driving style, temperature and climate conditions. Depending on the system – ECO mode or ECO+ – you'll benefit from optimized shift points and lock up control in the automatic gearbox, as well as the introduction of a Start/Stop function. ECO-climate will change climate control settings and auxiliary loads, while ECO-coast functionality helps the driver to conserve the kinetic energy of the vehicle by enabling it to coast, not unlike the old freewheel applications on manually-equipped cars.
The above, of course, is but a sampling – we hope you get the idea. Whether the mechanism is simple or sophisticated, the end goal is similar: Reduce the fuel consumption of the internal combustion engine. And while you increase its efficiency you also, by extension, extend its relevance.