2021 Chevrolet Silverado and GMC Sierra Lose 1 MPG Thanks to 1 Unusual Situation

Since late last year, both the 2021 Chevrolet Silverado and the GMC Sierra have experienced unusually high demand. While this is a great problem for General Motors, low supply has made it difficult to fulfill most of these new orders. Adding an unusual twist to this situation is the computer chip shortage across the entire auto industry.

According to Road & Track, the remaining 2021 versions of these trucks will ship without an active fuel management computer module. As a result, these trucks will become less efficient by 1 MPG on average. While this sounds like a downside, it could be a blessing in disguise.

Why are the Chevrolet Silverado and GMC Sierra less efficient?

A red 2020 Chevrolet Silverado Diesel full-size pickup truck travels on a four-lane highway past pine trees and a snow-capped mountain
2020 Chevrolet Silverado Diesel | General Motors

According to Automotive News, the only difference under the hoods of the 2021 Chevy Silverado and GMC Sierra is the lack of an active fuel management computer module. While this seems like a relatively small component, it runs the truck’s cylinder deactivation system.

As GM Parts Online reports, the system allows certain trucks to disable half of the engine’s cylinders at lower RPMs. This system can improve the truck’s overall fuel economy by up to 7.5 percent. However, this system is only available in trucks equipped with GM’s 5.3-liter naturally aspirated V8. This applies to trucks that feature both the six-speed and eight-speed automatic transmissions.

Additionally, this newest 2021 Chevrolet Silverado and GMC Sierra update will only result in the loss of 1 MPG on average, not a major difference for owners. If you’re thinking of buying a truck with GM’s larger 6.2-liter engine, you’ve got no worries. However, this deleted module might actually create a benefit for these trucks.

This might actually be a benefit to GM’s pickup trucks

A black 2021 GMC Sierra SLT four-door pickup truck towing a boat on a two-lane highway in the mountains
2021 GMC Sierra SLT | General Motors

As GM Parts Online points out, 2021 Chevrolet Silverado and GMC Sierra trucks equipped with this cylinder deactivation system might face more issues. This is because the system has reportedly previously contributed to oil consumption issues in these trucks. According to GM Parts Online, this is seen in engines that consume more than one quart of oil every 3,000 to 5,000 miles.

While these issues aren’t exclusive to the 2021 Chevrolet Silverado and GMC Sierra, it largely affects trucks that spend most of their time on highways. This is because the system sprays oil onto the pistons via an oil pressure relief valve.

According to GM Parts Online, this extra oil can burn up and cause build-up on the pistons and rings. Once this becomes severe, the problem can contribute to more oil consumption and eventually engine damage.

While General Motors issued what GM Parts Online calls a “partial fix” for these trucks, some owners modify them to remove or disable this system.

What about diesel-powered trucks?


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While this system won’t be in some 2021 Chevrolet Silverado and GMC Sierra models, the update only affects trucks with the 5.3-liter V8. As a result, all of the diesel-powered variants remain unaffected by this newest issue. Since this shortage affects 2021 model trucks, Automotive News estimates it will end toward the end of this summer when the 2022 models arrive.