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GM explains year-over-year MPG shifts, expected to draw up compensation plans for owners

As other automakers have in the past, GM will need to toss a little cash "on the hood" to make up for overstated fuel economy figures.

This could pass for a 2016 Buick Enclave, but it's actually a 2014. It's...kind of an old ute.

Antuan Goodwin/Roadshow

Even when vehicles are largely unchanged year over year, occasionally the EPA will come back with different fuel-economy figures. Some of it could be linked to new equipment (adding weight, therefore sacrificing economy), but occasionally, there are other factors at play, which is currently the case with General Motors.

Last week, GM claimed it had overstated fuel economy on three 2016 vehicles -- Buick Enclave, Chevrolet Traverse and GMC Acadia. This week, GM explains why that happened.

"New emissions-related hardware in the [Enclave, Traverse and Acadia] required new emissions testing for these vehicles," said GM spokesman Nick Richards in a statement. "The fuel economy data from these tests were not captured in calculations for EPA fuel economy levels for the 2016 model year Traverse, Acadia and Enclave (causing 2016 model year fuel economy numbers to be overstated)."

GM claims the error was picked up as engineers worked on next year's window stickers, at which point GM alerted the EPA and started making the switch to the proper, albeit lower numbers. Vehicles with the improper figures on their window stickers cannot be sold until the correct ones are applied.

Once that's done, it's time to focus on making things right for the customers who bought vehicles with incorrect fuel-economy numbers. Reuters reports that GM will reportedly compensate some 130,000 owners. This follows in the footsteps of Hyundai/Kia and Ford, both of which have had to pony up in the past for overstating fuel economy on their window stickers.

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