Because they have the same powertrains, it's possible previous model years could also have inaccurate mpg ratings.
[UPDATE]: A General Motors' spokesperson provided Motor1 with the following statement to explain the fuel economy discrepancy:
"New emissions-related hardware in the 2016 Chevrolet Traverse, GMC Acadia and Buick Enclave, required new emissions testing. That data was not captured in calculations made for EPA fuel economy labels and caused 2016 model year fuel economy numbers to be overstated by 1-2 miles per gallon for these vehicles. Including these new data yields fuel economy results of 15/22/18 – FWD and 15/22/17 – AWD. This error was discovered as GM engineers worked on the 2017 model year labels, and was quickly reported to EPA. We continue to work with the EPA on this issue."
General Motors’ stop sale and recall on the 2016 Buick Enclave, Chevrolet Traverse, and GMC Acadia for overstated fuel economy could grow to encompass an estimated two million earlier examples of these crossovers. Consumer Reports has alleged that after looking at its mileage data and information from the Environmental Protection Agency, the crossovers’ numbers may have been wrong since as early as 2007.
These three CUVs, plus the discontinued Saturn Outlook, use GM’s Lambda platform and a 3.6-liter V6. Consumer Reports asserts the 2016 model year examples aren’t significantly mechanically different than the earlier ones, but the revised fuel economy after this campaign drops their numbers compared to previous model years. For example, the updated mileage puts all-wheel drive examples at 17 mpg combined, but they had 19 mpg EPA ratings just last year.
As further justification for this claim, Consumer Reports says its own data backs up the previous model years’ fuel economy rating being too high. For example, the vehicles from 2007 and 2008 have delivered mileage 3 mpg below the EPA ratings in the publication’s testing.
GM announced on May 13 that the 2016 model year CUVs had a misprint on their fuel economy labels, which showed them getting 1-2 miles per gallon more than what was accurate. A stop-sale campaign affected 60,000 examples still at dealers, and the General promised a later recall for several thousand more that it already sold to customers. A spokesperson blamed the problem on an incorrect “data transmission,” and the automaker expected to have new window stickers for these vehicles by May 17.
In the age of scandals like those from Volkswagen and Mitsubishi, automakers’ fuel economy and emissions are under tighter scrutiny. However, there’s not yet proof of Consumer Reports’ allegation that GM misstated these CUVs’ mileage for years. The company also denied wrongdoing to the publication, and Motor1 has reached out to the carmaker for more information.
Source: Consumer Reports