This technology "turns off" some of the engine's cylinders when they are not neededChecked 2026-08-12
Cylinder deactivation
A system that shuts down some cylinders when the engine does not need them.
Also called: AFM · DFM · MDS · VCM · Active Fuel Management · displacement on demand
What it means
Definition
The DOE describes the principle: this technology turns off some of the engine's cylinders when they are not needed, such as at steady cruise. GM's service documentation describes its own version — Dynamic Fuel Management is recognized as active fuel management technology with the additional ability to deactivate any combination of cylinder valves for an internal combustion engine. Manufacturers each brand it differently: GM's AFM and DFM, Chrysler's MDS, Honda's VCM.
Why a buyer cares
What it changes
It is factory equipment rather than a modification, and it changes which components exist in the valvetrain — which is why estimates on these engines can name lifters and valve hardware that a conventional engine does not have.
In practice
Where you meet it
In spec sheets and window stickers under a brand name, in the owner's manual, and on estimates naming lifters or the deactivation hardware.
Two things that look alike
Not the same as
A misfire is a fault; a deactivated cylinder is switched off deliberately by the engine computer.
Read next
Related terms
Where this comes from
Sources
Dynamic Fuel Management (DFM) is recognized as active fuel management technology with the additional ability to deactivate any combination of cylinder valves for an internal combustion engine.Checked 2026-08-12
The GM quote comes from a document filed in an open NHTSA investigation into these lifters. Cite it as manufacturer service text; do not imply the investigation's outcome.