Gaming The EPA Gas-Mileage Tests: How It Really Works

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2013 Ford C-Max Hybrid, Los Angeles, August 2012

2013 Ford C-Max Hybrid, Los Angeles, August 2012

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Every now and then, EPA gas-mileage ratings--and cars that notably fail to achieve them in real-world use--burst into public awareness.

Hyundai and Kia had to agree to reduced ratings and send refunds to buyers after admitting to testing-procedure errors following an EPA investigation.

But do manufacturers really game the test cycles?

An interesting thought piece on Road & Track by ubiquitous writer Steve Abrams touches on the topic.

The 4-page article notes the increased level of electronic vehicle-control systems that sit between the driver and the car. They interpret driver requests for power, braking, or cornering--and decide which vehicle systems to activate, and to what degree, to fulfill the driver's requests safely.

It ties those systems together with future possibilities for autonomous driving by cars, and the challenges for engineers of designing cars that actually attain their EPA ratings.

Because the more sophisticated those electronic control systems become, the more opportunities there are for engineers to map some of their parameters directly against the known, standarized EPA tests.

As Abrams says:

Engineers know exactly how their vehicles will be evaluated. They know exactly how fast the car will go, and how long and how quickly it will accelerate or decelerate.

When engineers program the control logic, they can monitor parameters that correspond to the test cycles, such as speed, acceleration and pedal position, and select the gear ratios, throttle positions and air-fuel ratios that will deliver the minimum possible fuel consumption.

What this means in practice is that the car can be programmed to operate most economically under the various acceleration curves and drive cycles of the EPA tests--including three new tests added in recent years to the well-established city and highway cycles.

Those test conditions are, by now, archaic, with very gentle acceleration and low maximum speeds. So the EPA applies "adjustment factors" to bring them closer to real-world results, which usually works for gasoline cars.

Hybrids, however, are a different story. The amount of time the vehicle operates under electric power has a major effect on its gas mileage; the more it runs only on electricity, the less gasoline is burned.

And that appears to be the core of Ford's recent problems with its new 2013 Ford C-Max Hybrid and 2013 Ford Fusion Hybrid.

Both are selling well, based in part on the lure of their 47-mpg combined EPA ratings.

Widespread media coverage, however, has pointed out that drivers in the real world rarely achieve anything close to 47 mpg in either car.

The C-Max Hybrid seems to average 36 to 40 mpg, the somewhat more aerodynamic Fusion Hybrid 36 to 42 mpg.

Those are still remarkably high numbers for a compact hatchback and a mid-size sedan, which needs to be emphasized.

2013 Ford Fusion Hybrid, test drive, Catskill Mountains, NY, Mar 2013

2013 Ford Fusion Hybrid, test drive, Catskill Mountains, NY, Mar 2013

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But they're well below the 10-percent margin that most buyers seem to allow on either side of the EPA combined rating. The EPA is now investigating.

As Abrams notes, automakers face a major challenge: "Once a vehicle is sold, engineers have no control over where it’s driven and under what conditions."

Ford's 60-kilowatt (80-hp) electric motor in the latest generation of the hybrid system used in both 2013 models is apparently just powerful enough to allow lots of electric-only operation under the EPA test cycles.

In the real world, though, the combined 188 hp of the engine and motor together (40 percent more than the 134 hp of a 2013 Toyota Prius) lets drivers accelerate much harder--and burn much more gasoline doing so.

"Your mileage may vary," it seems, has never been so true.

Is programming the car's powertrain controls to maximize test-cycle results gaming the system?

Should the EPA try to change its test cycles entirely?

Or is it the driver's responsibility to maximize gas mileage by using just a fraction of the car's total available power?

Leave us your thoughts in the Comments below.


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Comments (10)
  1. I would really like to see the EPA come up with testing that is more in-line with the results seen on Fuelly. We need to eliminate this problem with "some" hybrids not being close to their real world values and many Diesels exceeding EPA numbers.

  2. While we're at it let's insist manufacturers increase the accuracy of fuel efficiency gauges. As much as I love my Prius, the GenIII gauge is approx. 5% optimistic. While I still have no trouble beating the EPA numbers by hand calculations. It's a let down to see a 65mpg (indicated) tank turn into a 61.75mpg tank when you divide miles driven by gallons pumped.

  3. Excellent point. Most owners use the gauge as a guide for their own reporting, typically.

    EPA should crack down on that gauge.

  4. I think the EPA should set standard parameters for hybrids, like having the same SOC on the battery at the end of the testing as in the beginning. This will prevent excess usage of battery power versus gas engine, thereby gaming the results the test may allow for the battery to be depleted.

  5. Should EPA change its testing methodology? No, if the differences in results are based on drive choice (e.g. acceleration). However, the results should include factors that influence results.

    I get 25% better mileage on the family prius, compared to my spouse. Acceleration and keeping up with traffic (to avoid being cutoff) explain the difference.


  7. I agree with JoAnn, I'm also considering a Ford hybrid but not under the current circumstances and not until it's investigated. Hopefully it'll resolve soon, the other choices are starting to look pretty attractive, if only the plug-ins got better range.

  8. With all the modern electronics, I prefer an "EPA mode". Required in all cars and buyers can easily set the car in EPA mode and reproduces the fuel efficiency themselves. If it doesn't match the EPA mpg in EPA mode, then it has reason to sue. All cars will be able to match the slow EPA requirement. Anything more than that belongs to "normal" and "sports" mode.

  9. Also, EPA can adjust the hybrid testing by requiring an empty battery to start and complete all 5 cycles in a single test.

    It will always be more accurate if the test is extended to 50 miles intead of 11 miles to match the daily requirement of American drivers.

  10. We should adopt the UN ECE reciprocity standards which most other major countries, including Japan and all of Europe, are using. Much cheaper, no need to federalize, many more cars instantly available to (and from) USA.

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