An Active Fuel Management system can save you a lot of money on fill-ups. It also comes with a different set of troubleshooting and repair steps. Knowing if you have one of these systems on your vehicle is important, and it’s not too hard to find out.
Start by looking for AFM information in your car’s owner manual. Next, look at the dashboard for a “V4” symbol or “AFM” light. Check for an AFM badge on your engine, and look for specialty lifters in the #1, #4, #6, and #7 spots. Cars made before 2007 don’t have Active Fuel Management, and only GM vehicles have AFM or DFM.
In this beginner’s guide, I’ll explain everything you need to know about Active Fuel Management. I’ll outline what it is, how it works, some drawbacks, and how to tell if your vehicle has Active Fuel Management.
What Is Active Fuel Management?
Active Fuel Management, or AFM, is a system that comes from GM. Back in ’05, their engineers were looking into ways to improve the fuel efficiency of their thirsty V8 engines.
They came up with AFM, which can also be called cylinder deactivation. This system intermittently turns off half the cylinders in your engine. As a result, your V6 engine will run like a V3 or your V8 will run like a V4.
The theory seems simple enough, and it really works in application. By using half the engine, the vehicle will produce much less power and energy, but it will use much less gas.
The heart of the AFM system is knowing when to turn it on and off. If you’re coasting through a city and not towing anything, there’s a good chance that the AFM system is live. When you floor it or you’re on highway conditions, then the AFM will turn off and all cylinders will be firing.
For a V8, cylinders #1, #4, #6, and #7 will always be the ones that get turned off through AFM.
Defining Dynamic Fuel Management
GM didn’t want to stop there with AFM. They developed Dynamic Fuel Management (DFM) which took the theory one step further.
In DFM, the number of cylinders that get turned off will change. A complex algorithm determined which cylinders and how many cylinders should be turned off. It goes based on the throttle application, speed, weight being towed, and a few parameters that they’re not so vocal about.
GM’s engineers claim that their DFM system runs through the algorithm 80 times per second. As a result, you’re getting a truly optimized fuel economy.
It’s worth noting that DFM doesn’t shut off the same four cylinders each time. This will come up later.
With this shift, GM had to come up with new firing patterns. It’s a whole lot easier to convert a V8 to a V4 and establish a new firing pattern. It becomes exponentially harder when the number of cylinders is changing by the millisecond.
Where Is AFM or DFM Typically Used?
AFM or DFM is reserved for V6 or V8 engines. It needs to be a V-shaped engine due to the symmetry that those engines have.
It’s also only used on GM vehicles: Cadillac, Buick, Chevrolet, Hummer, and GMC.
Which Vehicles Have Active Fuel Management as Standard?
Since this was a GM development, there’s some good news: only vehicles in the GM family have AFM or DFM.
The following GMC and Chevrolet vehicles come with Active Fuel Management as an option for one or more of their trim levels:
Also, an AFM is offered on Buicks and Cadillacs, like the ones below:
- Cadillac CTS
- Cadillac ATX
- Cadillac XT5
Drawbacks of Active Fuel Management
An AFM system is great because it can save you a lot of miles per gallon. You’ll go further on each fill-up, and you’ll save money on gas. However, there are some reasons to dislike an AFM system in your vehicle. Here are some of the bigger drawbacks.
Extra Wear on 4 Cylinders
The biggest critique of this system is that the four cylinders that are always running will wear much faster than in a standard V8.
Think about it — four cylinders have to do the work of eight. The worst part is that the cylinder wear won’t be even across the engine block. This can result in strange firing issues and a premature rebuild of your engine.
If all eight wore at the same rate, it wouldn’t be such a big deal.
This problem doesn’t exist on DFM engines, since it cycles which cylinders get turned off.
Another System to Worry About
AFM is another system that you have to troubleshoot and repair if it breaks. If one of the active lifters messes up or doesn’t stop in time, then your engine will be in trouble. This can lead to reliability issues.
However, I’ve only heard good things about the longevity of AFM systems, and they don’t typically break down like this.
By design, an AFM will drop your vehicle’s performance when it’s turned on. This means that stomping on the gas pedal will have a delay before you get the power. First, the engine needs to turn on all the cylinders, then it can start churning faster.
When you’re driving around the town, you might get annoyed at the extra waiting.
A Rougher Ride
I’ve been in cars that ran AFM systems, and you can actually tell when it kicks on. The ride gets a little rougher and you’ll notice more shakes. If you’re not in tune with your vehicle when you drive, then you don’t have to worry about this.
It also doesn’t amount to any big mechanical issues beyond the annoyance of dealing with a shaky ride.
Disabling The AFM/DFM System
If you find the AFM/DFM system a bit too much, are concerned about excessive wear & tear on the internal engine components, and would like a minimally evasive way to simply have the engine running at full capacity without having to reprogram anything or void warranty well you’re in luck.
There’s a device from Range Technology that will allow you to simply hook up a device via the OBDII port. It’ll prevent the cylinders from dropping which prevents the shuddering feel and allows all cylinders to run like normal at all times.
This is a really great device that is essentially plug-and-play and is easy to install.
How to Tell If a Vehicle Has Active Fuel Management
Knowing if you have Active Fuel Management is good for a few reasons. For one, you’ll learn more about your vehicle. It can also help with troubleshooting later on. If things feel sluggish, it could just be your AFM.
In addition, it’s critical for people who don’t like AFM and want to disable it.
Just listening to a car revving or looking at one at a red light won’t be enough to tell if it has Active Fuel Management. It’s not like that system that turns off your engine when you come to a stop. The cylinder firing sequence happens so quickly that you’ll never notice the difference.
Regardless of your reason for knowing why here are some steps to find out if your vehicle has active fuel management.
Look at the Owner’s Manual
The best suggestion I can make is to start with your owner’s manual. There’s so much useful information in there.
When it comes to AFM, you’ll see it pop up a few times in the manual. Go to the very back of the book, look in the appendix, and find “AFM” in their alphabetical breakdown. Follow that to the printed page number and viola.
You could also look in the dashboard indicator section and see if you find anything about AFM.
Look for an AFM or DFM Light
Speaking of dashboard indicators, this is the next-best place to check. When your AFM or DFM is active, you should see a light shining on the dashboard that tells you.
You can see all the lights on your dashboard by turning your car into accessory mode. This can be done by putting the key in the ignition, and turning it until points to the “ON” position, without cranking the engine and turning on the car fully.
If you have a push-to-start, then don’t press the brake pedal and push the ignition button. It will turn on the accessory mode.
Scan your dashboard to look for this light. GM uses different symbols for their different vehicles, so it might not be obvious which one you’re looking for.
Check the Engine
If you pop your hood and look at your engine, you should get a hint. There might be text on the cover that says “AFM” or “DFM”. GM doesn’t include this on all the vehicles that have AFM, but they do for some.
The AFM or DFM logo will be near the valve covers or perhaps by the intake manifold.
Ask the Dealer
If you’re still lost, maybe you can call a local dealership. They typically have a sheet of statistics about all of the cars they sell.
If you recently bought the vehicle, then you’re in luck — they probably have plenty of information and they can tell you.
But, if you bought the car used, it’s a different story. They likely won’t have the information to help you out.
Whenever I have a car problem that I can’t figure out, I’ll hit up Google. If you type in your vehicle’s year, make, model, and “active fuel management”, then you might get linked to a forum post that answers your question.
If you are curious about your vehicle’s AFM system, there’s a good chance that someone else is as well. They might have put some information on the Internet that can help you.
Consider the Date
If your car is older than 2007, I can guarantee that you don’t have Active Fuel Management. How? Because it wasn’t invented before then.
Now, that doesn’t guarantee that any GM car after 2007 has AFM, but it guarantees that any stock vehicle made before 2007 doesn’t have AFM.
Find a “V4” on the Dash
A lesser-used icon to look for is a “V4” somewhere on your dash. This is only used in GM vehicles that have V8 engines, and I’ve never seen a “V3” logo anywhere, so it might just be for V8s.
Either way, the V4 light should turn on when your AFM activates. This doesn’t happen on vehicles that have DFM, since the number of active cylinders can vary so frequently.
Check the Lifters
Since cylinders number 1, 4, 6, and 7 get turned off when AFM is activated, check the lifters in these four cylinders.
They will look much different than the lifters in 2, 3, 5, and 8. They’ll have springs, and engravings on the top, and they’ll be a lot taller. The difference should be immediately obvious if you have AFM.
By this point, you should know if your vehicle has Active Fuel Management. This is a great way to save money on gas, and it works really well. There are no extra maintenance steps that you need to know, just keep AFM in mind next time you need to troubleshoot a shaky ride.