General AFM/DFM Questions
We've compiled some of the most common questions about active and dynamic fuel management as well as how to go about deleting or disabling them.
What is AFM & DFM?
AFM and DFM are fuel management systems used on GM's V8 and V6 gas engines to improve fuel economy. These systems increase fuel economy by 5%-7% by deactivating cylinders under specific conditions. Active fuel management disables four cylinders in V8 engines and two cylinders in V6 engines, effectively operating as a V4 engine. Dynamic fuel management can deactivate a wider range of cylinder combinations and operate with as few as two cylinders, or V2 mode.
Is Displacement on Demand (DoD) different?
Displacement on Demand was the initial marketing term used by GM when it was initially released in the mid-2000's. GM eventually re-branded DoD as active fuel management, or AFM.
What's the difference between AFM vs DFM?
DFM is the more advanced successor to AFM. Vehicles equipped with DFM can operate with as few as 2-cylinders activated, whereas AFM can only deactivate four cylinders in V8's and two cylinders in V6's, operating as a V4. DFM on the other hand has 17 different firing combinations.
From a hardware standpoint, vehicles with AFM have specialized lifters and oil control valves only on the cylinders that can be deactivated - so on V8 engines only the specific 4-cylinders have the capability of turning off. Engines with DFM got the oil control passages integrated into the block with all eight cylinders getting the specialized lifters and control valves.
What are the benefits of AFM and DFM?
The sole benefit of these fuel management systems in the increased fuel economy. AFM has been tested to improve fuel economy by 5%-7%. GM claims that DFM can increase fuel economy by 5%-20% - with the larger range being attributed to the numerous different firing sequences that are possible.
What are the downsides of AFM & DFM?
The biggest problems these two systems cause from a reliability standpoint is lifter failure and excess oil consumption. Overall, here are the problems they cause:
- Stuck and collapsed lifters
- Excess oil consumption
- Hesitation during acceleration
- Rough transmission shifts
- Overall less smooth driving experience
- Engine failure from oil consumption/low oil levels
Ultimately, these fuel management systems save a bit of money in fuel but commonly lead to very expensive repairs due to lifter failure. Outside of reliability issues they do create some performance problems with acceleration and shifting.
Is DFM better than AFM?
DFM provides potentially better fuel economy savings but that doesn't necessarily make it better. Per tests, DFM is activated 60% of the time compared to 52% for AFM which leads to faster valvetrain wear. Furthermore, every cylinder on a DFM engine is equipped with the specialized AFM/DFM lifters that are prone to failing so you have 8 potentially problematic cylinders instead of just 4, or 2 with AFM.
What cylinders are deactivated?
On V8 engines with AFM cylinders 1, 4, 6, and 7 are deactivated. Vehicles with the LTA and LT2 engine codes instead deactivate 2, 3, 5, and 8.
On V6 engines with AFM cylinders 3 and 6 are deactivated.
On DFM engines, any one of the eight or six cylinders can be deactivated.
Which system is more problematic?
Ultimately, AFM has so far been the more problematic system but this is predominantly because it's used on older engines. DFM equipped engines have experienced more issues at lower mileages, it is just used on a smaller subset of engines that are much newer. Lifter failure tends to occur at higher mileages and AFM-equipped engines are just older. We suspect DFM will become a more problematic system once it's been around longer and vehicles start getting to the higher mileage levels.
How can I tell if my vehicle has AFM or DFM?
The easiest way to tell is by running a VIN verification and confirming which engine you have - and then confirming what engines use AFM and DFM.
Most AFM equipped vehicles have a dashboard setting that will display fuel economy and a V8/V6 Mode or V4 Mode badge on the bottom right. However, this isn't a feature available on every vehicle and 2019+ models with DFM do not have a dashboard feature to tell.
If you aren't sure if your engine has AFM, DFM, or neither then contact us and we can help you.
What's the best way to get rid of AFM/DFM?
There are three different ways to prevent the problems caused by active and dynamic fuel management:
- Disable it with a disabler
- Tune it out (reprogram the ECU)
- Fully delete the hardware (and then tune it out)
The easiest and best option is to use a disabler device, like our Boost AFM & DFM Disabler. It is a simple plug-and-play solution that can be undone by simply unplugging the device, which will leave no trace of it ever being there.
Reprogramming the ECU via tuning means you either need to buy a programming device, or you won't have the ability to undo it without taking it back to your tuner. It's more expensive and not as simple or undo-able.
Deleting all the hardware is the best way to completely mitigate lifter failure. But it costs thousands of dollars in parts and labor and then requires reprogramming and tuning so this is the most complicated and expensive option.
FAQs on Disabling and Deleting AFM/DFM
These questions focus more generically on active and dynamic fuel management. For questions about our device specifically, check out the FAQ section on our product listing which answers a bunch of questions about our warranty, how to use our device, and more.
What are the long-term effects of disabling fuel management?
AFM & DFM disablers have been on the market for about 5 years now, and they have been being disabled via tuning for many years longer than that with zero long-term consequences, outside of the fuel economy changes. It is healthier and better for your engine to not have the systems activated, actually leading to improved reliability over the long term.
Will disabling or deleting it reduce fuel economy?
The majority of users experience zero decreases in fuel economy or very minimal decreases around 0.5mpg. Users who do virtually all of their driving on the highway experience a slightly larger decrease around 1mpg.
In some cases fixing all of the hesitations, rough shifting, and other issues caused by AFM/DFM actually leads to slightly better fuel economy.
Ultimately, most people experience 0.0 to 0.5mpg decreases.
If you drive 12,000 miles per year a decrease of 0.5mpg costs you $54 per year, assuming a fuel cost of $3.50/gallon. $54 per year is worth saving the potential $2,000 to $5,000 repair bill from failed lifters, and will save you money on oil caused by the excessive oil consumption making it worth it in our opinions.
Will disabling it guarantee my lifters won't fail?
Disabling AFM and DFM will significantly reduce the likelihood of lifter failure. However, the technology and specially-designed lifters are inherently flawed and can still fail, especially if the disabler is installed on a vehicle that has already driven tens of thousands, or hundreds of thousands, of miles with these systems activated.
Ultimately, it reduces lifter failure significantly and can also fix or reduce oil consumption issues, but it does not completely prevent the problem from happening. The only way to completely prevent it is by doing a full delete.
Does it void vehicle warranty?
Unlike reprogramming the ECU or fully deleting the system, a plug-and-play disabler device does not void factory warranty. Devices like ours simply relay messages to the engine's computer telling it not to engage AFM or DFM. They do not change the factory programming and therefore don't void warranty. However, it is recommended to unplug the device before taking your vehicle to the dealership to avoid any potential conflicts. There is no evidence that the device has been plugged in once it is removed.
What are the reasons to disable AFM & DFM?
The two primary reasons are:
- Reliability
- Performance
Disabling fuel management will decrease the likelihood of lifter failure and excessive oil consumption. From a performance standpoint it will reduce the hesitations while accelerating, create a smoother driving experience, and improve throttle response.
