Active Fuel Management

Active Fuel Management (AFM) is a GM system that was developed in 2005 to help improve the fuel economy from some of their engine applications. The philosophy behind AFM, otherwise known as displacement on demand (DOD) or 4-cylinder mode, is to deactivate certain cylinders when the engine's full power is not required, effectively converting the V8 engine into a more fuel-efficient V4. Some of the popular models that are equipped with AFM include Tahoe, Yukon, Suburban, Sierra, Silverado, and Escalade. 

Countless vehicles equipped with AFM have experienced problems ranging from low oil messages all the way to complete engine replacement due to issues pertaining to the Active Fuel Management system. Symptoms are generally more prevalent in those vehicles with aluminum engine blocks, but can also occur in iron block engines.

Common issues include:

  • Oil consumption greater than one quart per 1000 miles
  • Combustion chamber deposits resulting in excessive pinging and fuel mileage drop
  • Lifter and/or camshaft failure
  • Engine failure due to ring issues

The premise behind AFM is that most of the time, vehicle owners have more power than they need. Many consumers choose V-8 engines for driving performance or towing, yet during everyday driving, that powerful engine operates at a fraction of its capability. This reduces engine efficiency, which means less than optimal fuel economy. Under AFM, when only a fraction of the available power is needed to keep the vehicle moving, the fuel delivery to four of the eight cylinders is switched off and a solenoid system collapses the valve lifters to reduce the pumping losses and improve fuel efficiency.

While GM has claimed up to a 12% fuel economy improvement due to the AFM system, we have seen the aforementioned negative side effects but also benefits from disabling it.

Common benefits of disabling the AFM:

  • Improved performance due to all cylinders in your V8 engine remaining active, providing more power and torque when you need it most.
  • Enhanced reliability by avoiding excessive oil consumption, lifter and camshaft issues, and uneven engine wear.
  • Reduced maintenance costs by avoiding the potential problems associated with the AFM.
  • Enhanced resale value due to increased appeal to potential buyers in the used truck market because to its reputation for improved reliability and performance.

The 2007-2013 Gen-IV vehicles equipped with AFM are particularly troublesome. Starting with the 2014 models, the AFM has improved and we have seen fuel savings without the negative side effects. While there is a small percentage of 2014+ vehicles we have tuned that have experienced these negative side effects, the vast majority have not.

From a tuning perspective, our recommendation is to disable the AFM on the 2007-2013 models while keeping it enabled on the 2014+ models. There are exceptions though. On the 2014+ models with larger aftermarket tires, there can be mileage losses or custom exhausts can cause exhaust droning. In those cases, we would recommend disabling the AFM.

We offer multiple tuning options that will allow for you to enjoy the vehicle that you love without having the obnoxious marketing gimmick getting in the way of that, ranging from a single item tune allowing for just one item to be adjusted all the way to our AutoCal tuning system, which will provide you with a full engine and transmission tune by email. In many cases, customers have reported back no mileage drop or even a mileage increase with AFM disabled!

If you'd like to speak with us more about this solution or proceed with a tune, please visit our Tuning Services page or our Contact Us page. Additionally, our frequently asked questions page has answers to many common GM and tuning related questions.

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