What is AFM on a Truck, and Why Should You Consider Disabling It?

If you’re a truck owner or enthusiast, you might have encountered the term AFM, which stands for Active Fuel Management. This technology, also known as Displacement on Demand (DoD) or cylinder deactivation, is a proprietary system developed by General Motors (GM) to enhance fuel efficiency by deactivating half of the engine’s cylinders under light-load conditions. But what does AFM mean for your truck’s performance, and why might you consider disabling it? Let’s delve into these questions.


Understanding Active Fuel Management (AFM)

GM has incorporated AFM, a fuel-saving technology, into many of its vehicles, including trucks. The system works by shutting down half of the engine’s cylinders when the vehicle is under light-load conditions, such as cruising at a steady speed on a flat road. This reduces fuel consumption and can improve gas mileage by 5-7% under certain conditions.

The Impact of AFM on Performance

While AFM can enhance fuel efficiency, it can also affect the vehicle’s performance in several ways. For instance, some drivers find the sound of the engine running on four cylinders rather than eight to be annoying, especially if the vehicle is equipped with a louder aftermarket exhaust. Additionally, some drivers prefer to have the full power of all eight cylinders at their disposal at all times.

Another issue with AFM is that the lifters used in the system have a history of failing, which can lead to oil consumption problems. This is because the AFM system uses special lifters for cylinders 1, 4, 6, and 7, which are taller and have unique oil holes. When these lifters fail, it can lead to significant engine damage.

Disabling or Deleting AFM

Given these potential issues, some truck owners opt to disable or delete the AFM system. There are two primary ways to do this: installing an AFM Disabler or an AFM Delete Kit.

AFM Disabler

An AFM Disabler is an electronic device that plugs into the OBD-II port under the dashboard. It prevents the vehicle’s computer from switching to four-cylinder mode, effectively disabling the AFM system. This is a simple and effective way to turn off AFM and can also improve the vehicle’s exhaust sound. However, it’s important to note that a disabler device should only be used if the valvetrain is in good working order.

AFM Delete Kit

An AFM Delete Kit is recommended when an AFM lifter fails or performs performance upgrades. It replaces the AFM components with standard parts. When installing an AFM delete kit, you must upgrade to a non-AFM camshaft because the cam lobes in the four AFM cylinders are ground differently. You must also turn off the AFM system using a computer programmer or custom tuning. Additionally, it’s recommended to plug the pressure relief valve in the oil pan and switch to a standard-volume oil pump.


AFM is a fuel-saving technology that can improve gas mileage but may also lead to performance issues and potential engine damage. If you’re a truck owner considering whether to disable or delete the AFM system on your vehicle, it’s important to weigh the benefits of improved fuel efficiency against the potential drawbacks. Always consult a trusted automotive technician before making significant changes to your vehicle’s engine.

About the author, Laurence Perkins

Laurence Perkins is the passionate car enthusiast behind the blog My Auto Machine. With over a decade of experience in the automotive industry, Perkins has knowledge and experience with a wide range of car makes and models. His particular interests lie in performance and modification, and his blog covers these topics in-depth. In addition to his own blog, Perkins is a respected voice in the automotive community and writes for various automotive publications. His insights and opinions on cars are highly sought-after.