Do All Those Driving Modes Affect a Car's EPA Gas Mileage?

Technology is taking a lot of the "driving" out of today’s cars, whether with advanced safety nannies like lane departure systems or sports cars with advanced automatic transmissions.

But one piece of burgeoning technology promises to deliver better mileage at the push of a button.

It isn't just luxury cars that have these selectable driving mode buttons. Models as plebian as the Honda Civic and Dodge Grand Caravan have fuel-saving economy modes; others, like the Nissan Altima and Honda Accord, have Sport modes.

But do EPA ratings reflect this technology?

It depends.

These selectable driving modes can dial in mileage-saving economy settings alongside a Normal mode. Others have more options besides efficiency for Sport and sometimes Super-Sport modes. In turn, all can influence gas-pedal sensitivity, automatic-transmission shift patterns and steering feedback. Some Sport modes can even dial back an electronic stability system or hunker down an adaptive suspension to sharpen handling — and a number of economy programs, in turn, can restrain the air conditioning in the name of efficiency.

Such programs certainly affect real-world gas mileage. A more sensitive accelerator or kickdown-happy transmission often trades fuel efficiency for performance; relaxing those inputs with an economy mode, by contrast, guzzles less fuel and generally provides less excitement behind the wheel. The differences can be significant: In an unscientific mileage drive in 2009, we observed that driving in Sport mode could slash mileage as much as 11%.

How does the EPA take all of this into account?

"All EPA ratings are done in the Normal mode," Honda spokesman Chris Martin said of the Civic and Accord, which have Eco and Sport modes, respectively. "EPA ratings are trying to create an apples-to-apples comparison between models, which is best done in a default normal driving mode."

Honda is but one example. The EPA sent us a statement along with a 2009 policy document that said it would handle such driver-selectable systems "on a case-by-case basis." Here's how it shakes out:

  • If a car has various modes but defaults back to Normal whenever you turn the engine back on, the EPA draws its ratings from the Normal mode.
  • But vehicles that default to a fuel-saving mode at start-up — like the 2014 Jeep Grand Cherokee — set economy as the "predominant" mode from which the EPA bases its ratings, the agency told us.
  • If a car has multimode system that stays in whatever you last drove, the EPA may not be able to establish a "predominant" mode. In such cases, "the vehicle is tested in the various modes and the fuel economy results from the best and worst modes are harmonically averaged," EPA officials wrote. "For example, if a vehicle has a sport mode, normal mode, and economy mode, the fuel economy results of the sport and economy modes would be averaged."
  • Automakers can (and often do) submit customer surveys or technical data that show that customers use one particular mode most of the time — so if Honda determined that 80% of Civic owners drove everywhere in Econ mode, then it could request that the EPA rerate the Civic using economy-mode driving. If it's too early to assess the mode that drivers use most often — say, with a fresh redesign or introduction — then automakers can exercise "good engineering judgment" to determine what's predominant, the EPA said.
It gets more complicated when cars offer extra modes as an option. The Audi A4's Audi Drive Select system is optional, for example. So are the extra-sporty settings that come with sport packages in the Lexus IS (Sport S+) and BMW 3 Series (Sport+). The EPA says it treats those particular variants as separate cars, and as such, they must be tested as well. The results factor into an overall model's EPA numbers, but such variants rarely get their own unique EPA label. Agency documents also said automakers can win approval to test the two "most prevalent transmission settings," which suggests that optional modes may not influence EPA ratings much. Neither do unconventional modes, like Tow/Haul in a pickup or Snow in an SUV; the EPA documents said they can generally go ignored for the sake of mileage ratings.

The upshot? If your car stays in the mode you left it the last time you drove, chances are good the EPA window-sticker mileage reflects some or all of its driving modes. But if your car defaults back to a default mode, chances are the EPA mileage only reflects that mode. That's why those window stickers say, as always, that your mileage may vary.

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