What is AFM/DFM? An In-Depth Look

10 min read

What is AFM/DFM? An In-Depth Look

10 min read

What is AFM/DFM? An in-depth look.

Active Fuel Management (AFM) was a system GM engineers developed back in 2005 to help improve the fuel mileage from some of their V6 and V8 engine applications. AFM shuts off half of your engines cylinders to operate at a reduced power level to reduce fuel consumption when running in low load and cruise situations. By 2019, GM had developed Dynamic Fuel Management (DFM) which a smarter version of AFM. While AFM would shut-off the same cylinders every time the system would activate, with DFM, the engine has up to 17 different patterns it can run in depending on load and other inputs. With DFM, the engine can turn off two cylinders, four cylinders, or any of the eight it sees necessary to meet the current situation and demand.

Popular vehicles where you'll find AFM/DFM

  • Corvette
  • Camaro
  • Tahoe
  • Suburban
  • Silverado
  • Sierra
  • Yukon
  • Equinox
  • Traverse
  • Escalade.

On paper and even in the real world, AFM and DFM has shown some benefits when it comes to improved fuel mileage and GM has been able to claim 5-7% increases directly correlated to AFM. There have been studies held that back the claims with data and vehicle owners can attest to seeing solid mileage from their GM V6 and V8 engines, especially when compared to that vehicles counterpart from another brand. However, with all that said, AFM and DFM systems don’t come without pitfalls. Over time, some of the

Negative drawbacks to Active Fuel Management

  • Excessive oil consumption
  • Engine and transmission shudder
  • Premature wear to the valve train
  • Exhaust drone
  • Hesitation on acceleration
  • In some extreme cases, complete engine failure

So how does the system actually work? In the low load situations, the vehicles computer will send a signal to the engines Lifter Oil Manifold Assembly, which activates solenoids that open allowing oil to flow through special lifters housed within the ADM towers of the engine block. This oil then collapses the plunger inside the lifter, which won’t allow the lifter to engage the push rod, so the valves remain closed for that cylinder. Obviously, with the valves closes, no air can enter or exit that cylinder, meaning it provides no power. When engine load increases, the computer sends the signal back to the lifter oil manifold assembly to close the solenoids, oil bleeds off of the lifters and they return to natural operation and the cylinders begin contributing again.

Image from GMTech

With so many internal working mechanisms required to turn on and off thousands of times, it’s only natural that overtime these small pieces begin to wear and create problems down the road. It’s quite common for an AFM equipped engine to start seeing excessive oil consumption starting as early as 70-80,000 miles. There have been stories of as much as 2-quarts of oil burned in a basic 3000-mile oil change interval. This obviously affects engine efficiency, durability, maintenance costs, along with adding to other underlying issues like hesitation on acceleration, engine shudder, and a frustrating exhaust drone in the cab when running in low power modes.

Luckily for the GM owners everywhere, there is aftermarket support here that can help prevent some of these expensive repairs and failure modes. Range Technology of Ogden, UT developed a simple to install, end all cure all, for the troublesome Active and Dynamic Fuel Management systems. Their AFM/DFM Disabler module will simply plug direct into your vehicles OBD-II diagnostic port under the dash, automatically detecting the AFM/DFM system and disabling it for good. No programming required, no permanent changes to the vehicle, and best of all, no traces left on the PCM should you still be under a factory warranty. The AFM/DFM Disabler can be unplugged returning the vehicle to factory function in seconds and can be reinstalled just as easily once dealer warranty work is completed. One part number covers just about every applicable GM application from 2007-2020 and the module can be moved from one vehicle to another at any time.

The AFM/DFM Disabler is inexpensive and requires no time or effort by the owner to be installed. There is no learning curve or homework required.

Plug in the device, wait for the LED’s to power on, start your vehicle and drive.

It’s truly a plug and play resolution to potentially very costly repairs.


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