How and Why Do Automakers Cut Corners on Emissions?

Federal loopholes, error, and sometimes unlawful programing or testing could allow automakers to skew fuel economy and emissions numbers.

Clifford Atiyeh | 

Jan 9, 2023 | 4 min read

Volkswagen

Not every new car has been put through a gauntlet of government-administered emissions testing. Verifying every vehicles’ compliance with all safety, health, environmental, and trade laws would be too time consuming and costly for any federal or state agency, so the onus falls to the car’s manufacturer. For fuel economy and emissions ratings—which have a big impact on both your wallet and air quality—the U.S. government audits just one out of five car models each year.

With more than 300 models on sale, that means you’ll have to trust that automakers will tell you the truth.

It's Not All Bad

The Volkswagen diesel emissions scandal cracked the lid open on cheating automakers. VW admitted to installing software that could detect when its cars were being run on the testing cycle required by the Environmental Protection Agency (EPA). VW’s diesel engines operated cleaner in the lab and earned stellar results on paper, but in the real world, they polluted many times over legal limits.

Volkswagen paid billions to settle civil and criminal charges, including damages to customers (monetary compensation and buybacks), fines paid in various countries and including paying to build a national charging network in the U.S. Additionally, several VW executives have been charged and two have pled guilty and been imprisoned.

Like any agency, the EPA runs short on staffing and funds to properly do its job. It admits to only auditing between 15-20% of all new cars in a given year. Automakers know that if caught cheating, they face the wrath of government and class-action lawsuits which have the potential to sink their balance sheets.

The Process Allows Loopholes–But Automakers Take Them at Their Peril

There are workarounds permitted by the EPA that let automakers duplicate one model’s fuel economy numbers even if they are not identical. The EPA allows a high volume model within the weight class with the same engine and transmission to be used to determine fuel mileage of lesser-volume models.

Ford took flak in 2013 when its C-Max wasn’t returning real-world fuel economy anywhere near its 47 mpg combined estimate. When probed, Ford admitted it used the same numbers from the car it did test, the Fusion Hybrid, because EPA rules allow an automaker to do so when the two vehicles use the same powertrain and share the same weight class. But Ford made an obvious mistake to rate a higher-riding hatchback with the same figures as its lower, sleeker sedan. The result: Ford had to recertify the C-Max from 47 mpg combined to just 43 mpg combined. Ford settled the lawsuit brought by 40 states on behalf of consumers against the automaker for false advertising. The $19.2 million settlement is meant to compensate owners for the extra fuel costs.

Hyundai and Kia simply didn’t test their cars properly. After touting 40mpg on many of its best-selling models starting in 2011, the companies were caught in a class-action lawsuit and a subsequent investigation by the EPA, after owners claimed they couldn’t come near the EPA estimates. By 2015, the companies settled for $210 million, compensated current and former owners for their added expenses, and had to revise estimates on 27 models. It was embarrassing but were it not for a lawsuit, Hyundai and Kia might have gotten away with such a major error.

The EPA requires automakers to rate fuel economy and emissions on the model's trim with the highest sales volume. When the Chevrolet Corvette entered the 2022 model year, it lost 3mpg on the highway estimate—a not insignificant 11% drop–compared to 2021.

Because the Z51 was the most ordered in 2021, Chevrolet provided the Z51 for EPA testing. However, the Z51 performance package comes with a unique rear axle. The engine spins faster in top gear because the rear axle has a shorter drive ratio for better acceleration, so it consumes more fuel. Chevrolet noted surprise at how many Corvette buyers stepped up to the Z51 package, which costs around $6,350 on its own.

Your Mileage (And Driving Experience) Will Vary

What works in a lab doesn’t always translate to the real world. For example, transmissions are usually programmed to upshift early, a technique that lowers engine revs and saves fuel on a test, when in normal driving it can inhibit performance. Auto stop-start systems gain points in the lab but can actually consume just as much fuel on the road due to constant use in traffic. All of a vehicle’s hardware and its software tuning can be tailored to ace tests. The best automakers know how to program their vehicles—legally—so they deliver the best blend of performance and efficiency.

Clifford Atiyeh

Clifford Atiyeh is an independent writer, photographer, and creative consultant. He has reported for dozens of websites, magazines, and newspapers in his 20-year journalism career, during which he has tested more than 650 new vehicles. His automotive expertise focuses on product development, market analysis, and the litigation and legislation affecting the industry. Clifford is vice president of the New England Motor Press Association and runs a marketing consultancy.