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If you've shopped for a new car in the past year or two, you may have noticed a new feature that's creeping into all sorts of models: The "eco button." Manufacturers are installing the little, illuminated squares of plastic in everything from hybrids to sporty coupes, high-horsepower sedans to V8-powered SUVs.

Ostensibly this new feature allows you to transform your vehicle into a green machine, selecting a driving mode that puts your car's abilities on a short leash -- but only at your choosing. Depending on the vehicle, in green mode the throttle won't be as responsive or the transmission will shift into a higher gear at lower rpms, or the electric systems will be tuned to reduce their energy draw.

Here are a few examples of how these eco modes affect the driving experience:

Chevrolet: The four-cylinder Equinox with a six-speed automatic transmission comes with an eco button that, when pressed, locks the transmission's torque converter at lower speeds and tells the transmission to shift to a higher gear earlier. It has no affect on throttle response.

Dodge: The 2011 Grand Caravan in eco mode will smooth out throttle response and upshift sooner in order to save fuel.

Honda: The CR-Z and Insight, both hybrids, have eco buttons and the feature will be present in the Fit EV to increase battery range. In economy mode for the CR–Z and Insight, the electric motor assist prioritizes fuel efficiency and the air conditioning system will reduce its overall load on the engine. The drive-by-wire throttle is optimized for smoother acceleration and maintains the lowest possible engine rpm, power and torque decline by four percent (except at wide-open throttle, which still gives full responsiveness), on the CVT-equipped models the transmission ratios are optimized to be higher relative to engine rpm, and when using cruise control the throttle employs a smaller opening angle whenever possible.

Hyundai: The Korean firm's eco offerings are shaded blue rather than green, so the Sonata has an Active Eco button and so will the coming Veloster. It modifies the transmission shifting schedule.

Infiniti: The 2011 Infiniti M – with a 5.6–liter, 420-horsepower V8 – comes standard with an eco button, but its operation can be enhanced if a buyer chooses the optional Technology Package. The standard setting changes throttle positioning and shift points. Get the upgrade, however, and you'll get the "Eco Pedal" (which can be turned on or off) that "provides feedback to encourage the driver to optimize fuel efficiency." Translation: The accelerator pedal pushes back a bit and vibrates underfoot when you're giving it the lead boot. "The feedback is slight," Infiniti says, "and can be easily overridden by the driver depressing further on the pedal."

Nissan: The Juke crossover has an Eco button, which adjusts throttle responsiveness and transmission mapping for the CVT. And in what seems like a case of miserliness heaped atop frugality, the electric Nissan Leaf also has an eco button. Pressing the Leaf's button has the same effect as the Juke, but instead of changing the transmission mapping – since it doesn't have a traditional transmission – it provides more aggressive regenerative braking, as well as reducing the use of the air conditioning compressor.

Toyota and Lexus: The Toyota Prius and Highlander Hybrid, and Lexus HS250, RX 450h, LS 600 hL and the coming CT 200h have switchable eco modes that tweak accelerator response and optimize the climate control. The Camry Hybrid also has a dedicated green mode, but it doesn't affect the throttle, it only adjusts HVAC system to improve fuel efficiency.

When it comes to quantifying the results of driving in these economy mode, manufacturers usually estimate a five- to ten-percent improvement, though Dodge said that the econ mode in the Grand Caravan is good for about one more mile per gallon. Do the math and a vehicle rated at 25 combined mpg will then get anywhere from 26.25 to 27.5 mpg. That's about the same improvement most people would see if they kept their car in a proper state of tune with the tires inflated -- or if they just drove a bit less aggressively.

Of course, you mileage will vary, as is the case with all measures of fuel efficiency, including the official ones done by the EPA. Which brings up another interesting point, which is that all the vehicles hauled off to the EPA's National Vehicles and Fuel Emissions Laboratory in Ann Arbor, Michigan, for testing will be revved on the dyno only in their normal operating mode. Even if a car is equipped with an button that adjusts the car's responses to increase fuel economy, the EPA never presses it to ascertain how mpg is affected.

There are plenty of reasons for this, prime among them that fuel economy and emissions testing protocols are so interrelated between the EPA, Department of Transportation and Congress that the proverbial butterfly shifting its wings in EPA headquarters at Federal Triangle could translate into chaos in the Capitol. But another reason is even simpler: It isn't clear who really uses the eco button, and how often, and why. Even the manufacturers aren't sure.

When we asked, only Honda provided us with an estimate, saying "our internal customer research shows that in the CR-Z, 50 percent of drivers use the ECO button (compared to Sport and Normal) as their primary driving mode." That's a healthy number, and while we have no proof of it, we'd tend to think that the usage stats for other cars wouldn't be that high. We suspect that buyers of the CR-Z, a small two–seat hybrid, are more inclined to use their economy driving mode than those who take home an eight–cylinder Infiniti M.

The other big question is why these buttons exist at all? Is it because car buyers really want them or has marketing taken over the movement? It's probably a dead heat. Buyers really are asking for features that will let them spend less at the pump, and eco buttons can save gas. If oil prices continue their climb, buyers' polite requests will surely turn into forceful demands. Nevertheless, drivers don't want to sacrifice speed or comfort or ride, at least not all the time. Hence the eco button, so you can go further, if a little bit slower. It might be marketing, but since it leaves things entirely up to you it is also, in the words of Kyle Bazemore at Infiniti, "the luxury of choice."

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    • 1 Second Ago
      • 3 Years Ago
      How many times are you morons going to keep rewriting this SAME STORY? In the past 8 months, you have done at least 27 so called "news" articles on this exact same issue. Is there that much of a shortage of newsworthy events in the world? If news is that hard to come by, try publishing some spelling and grammer lessons for people like "Harry Hurt" and your own illeriterate reporters.
      • 3 Years Ago
      anyone remember Cadillac's "4-6-8" ?
      • 3 Years Ago
      My daughter turned 16 last month and there was just no way we could afford to add her to our existing insurance policy. I started shopping around for new car insurance and found this site: ( http://tinyurl.com/InsuranceTip ) I just put in my ZIP code and received four quotes instantly after filling out your form. By comparing rates we were actually able to include my daughter in our new policy and not pay anymore per month for car insurance than we were originally paying for just me and my wife!
      • 3 Years Ago
      My daughter turned 16 last month and there was just no way we could afford to add her to our existing insurance policy. I started shopping around for new car insurance and found this site: ( http://tinyurl.com/InsuranceTip ) I just put in my ZIP code and received four quotes instantly after filling out your form. By comparing rates we were actually able to include my daughter in our new policy and not pay anymore per month for car insurance than we were originally paying for just me and my wife!
      • 3 Years Ago
      SCAM...I'll be Al Gore is behind this one
      • 4 Years Ago
      MHDJL, Thank you! I had this feature in my 1981 Eldorado. It made NO REALISTIC difference in my gas mileage, and was simply a problematic concept from the get-go. Unfortunately, this was before car warranties offered any type of real assistance to buyers. Many people got burned with this. They should have just recalled all of them and replaced the engines with trustworthy 350's but they didn't do a damn thing. The 368(8-6-4) wasn't a bad engine overall, but the transmissions GM paired them with were WORTHLESS. These were some of the bad years for GM, and the sting is still there for many buyers.
      • 4 Years Ago
      Tow comments. Hydrogen from water is great, except it takes more energy to seperate them than you recover from the resultant hydrogen. Secondly, the Caddy cylinder deactivation was called V8-6-4. It didn't work because electronics at the time (1980s) were not up to the task. Cylinder deactivation is now on many new engines, including Chrysler's Hemi and Honda's V6.
      • 4 Years Ago
      Why do some folks turn "comment boards" into Debates or lessons in English Grammar? Do they really feel a pressing need to be superior? Relax. This ain't no Ivy League lecture hall.
      David Devlin
      • 4 Years Ago
      My wife's Dodge 2010 Charger with the Hemi engine goes into ECO mode on it's own. When ever you are cruising about about 50 mph or above it shuts down 4 cylinders. So a V8 with upwards of 350 HP gets about 16 - 18 mpg in the city, and just short of 25 mpg on the highway. Don't even have to push a button, throttle response is always the same, the transmission works the same. We also have a 2005 Magnum that does the same thing, except it only gets 23mpg on the highway.
      • 4 Years Ago
      Softball Nut
      • 4 Years Ago
      No, They do nothing. Check with consumer report't test. Does not work. Try Hydrogen from water, it works.
      • 4 Years Ago
      Gimmicks like that will sell cars. The auto makers aren't dumb.
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