GM AFM & DFM Guides

AFM vs. DFM: What Did GM Improve, Is DFM More Reliable, and Should You Disable It?
Active Fuel Management and Dynamic Fuel Management share the same basic goal: reduce fuel consumption when an engine does not need all of its cylinders. Their control strategies, however, are not the same. Traditional AFM normally deactivates a predetermined group of cylinders under suitable light-load conditions. DFM expands the concept by making more flexible cylinder and combustion-event decisions based on the torque required at that moment. That makes DFM a meaningful engineering advancement over AFM. It does not prove that every lifter, oil-control, pushrod, camshaft, or valve-train concern has been... Read more...
GM AFM/DFM Repair and Diagnostic Guide: Tick Noise, Misfires, Lifter Problems, and What to Check First
A ticking noise, rough idle, or P0300-series misfire code on a GM V6 or V8 can be concerning. It can also lead owners to assume immediately that an AFM or DFM lifter has failed. That assumption may be correct in some cases—but it is not a diagnosis. AFM and DFM are coordinated electronic, hydraulic, and mechanical systems. Engine oil pressure, control solenoids or oil-control valves, switchable lifters, pushrods, rocker arms, valves, injectors, ignition components, sensors, and Engine Control Module logic all participate. GM engineering patents describe cylinder deactivation as an... Read more...
A GM LS-based V8 engine in a 2015 GMC Yukon Denali. AFM components such as the switchable lifters are located inside the engine and are not visible in this exterior engine-bay photo.
GM AFM and DFM Explained: How Cylinder Deactivation Works, Key Differences, and What Owners Should Know
Active Fuel Management is one of the most discussed—and often misunderstood—features found in many General Motors engines. Some owners know it as AFM. Others remember the earlier name Displacement on... Read more...