Active Fuel Management (AFM)—also known as Cylinder Deactivation—is GM’s variable-displacement engine technology. It's designed to improve fuel economy by allowing V6 and V8 engines to deactivate cylinders under light-load conditions, such as steady highway driving.
When deactivated, these cylinders are closed off and filled with trapped air, effectively turning them into air springs. This reduces energy loss through pumping, helping the engine run more efficiently while maintaining a smooth driving experience.
👨🔧 How AFM Works
🔧 Hydraulic Lifter Control
AFM uses a combination of solenoids and hydraulically-actuated lifters, located in the engine valley, to disable specific intake and exhaust valves. These lifters, supplied by Eaton and Delphi, temporarily prevent certain cylinders from firing, allowing the engine to operate in a leaner mode when full power isn't required.
🛢️ Oil Quality Matters
Because the AFM system relies heavily on precise hydraulic function, engine oil quality is crucial. Using the wrong oil viscosity or skipping oil changes can lead to improper operation—or even failure—of the AFM lifters. GM recommends using high-quality oil that meets their standards (typically SAE 5W-30) and maintaining regular oil change intervals.
🚀 Generational Evolution of Cylinder Deactivation
1️⃣ First Generation: Cadillac’s V8‑6‑4
GM's first venture into cylinder deactivation came in the early 1980s with Cadillac’s electronic V8‑6‑4 engine. While revolutionary, this system was ahead of its time and plagued with electronic issues, leading to its discontinuation.
2️⃣ Second Generation: Modern AFM Rollout (2005–Present)
In 2005, GM introduced modern Active Fuel Management with the Vortec 5300 V8 and gradually expanded the system to other engines like the LZ8 V6 and LS4 V8. These setups typically disable half the engine’s cylinders under light-load conditions. For instance, the 2010 Camaro SS (automatic) featured the L99 engine with AFM, capable of switching to four-cylinder mode while cruising.
3️⃣ Third Generation: Dynamic Fuel Management (DFM)
Debuting in 2019 Chevrolet Silverados, Dynamic Fuel Management (DFM) represents the next step. Instead of simply toggling half the cylinders on or off, DFM can deactivate any number of cylinders in various combinations for smoother performance and even greater fuel savings. It uses a strategy called Dynamic Skip Fire, developed by Tula Technology, and has earned recognition on Ward’s 10 Best Engines list.
⚙️ Pros & Considerations
✅ Fuel Efficiency: AFM/DFM systems can improve real-world fuel economy by 5–8%.
✅ Smarter Performance: These systems allow for full engine power when needed, and fuel-sipping operation during low-demand situations.
⚠️ Maintenance Sensitivity: Skipping oil changes or using the wrong oil can lead to lifter failures, rough engine operation, or costly repairs.
🔧 Real-World Example: When AFM Goes Wrong
Just because your engine is making a knocking sound doesn’t mean it's done for. We recently had a 2010 GMC Yukon come in with exactly that issue—a loud ticking noise coming from the engine bay. Surprisingly, the vehicle still drove well, wasn’t misfiring, but the check engine light was on.
After a thorough inspection, our technician removed the right valve cover and discovered the issue: the rocker arm on cylinder 4 was loose due to a failed AFM lifter.
This is a relatively common issue in AFM-equipped engines. When functioning correctly, AFM lifters deactivate cylinders to improve fuel economy. But if a lifter fails, it can cause valve issues, ticking sounds, and possible long-term engine damage if ignored.
The good news? The engine wasn’t destroyed. We replaced the failed lifter and related components, and the Yukon was soon running smoothly again—no engine replacement necessary.
🧭 Final Takeaway
GM’s journey from early cylinder deactivation efforts in the 1980s to today’s sophisticated DFM systems shows a commitment to combining performance with fuel savings. These systems give drivers the benefit of V6 or V8 power when they need it—and the fuel economy of a smaller engine when they don’t.
That said, staying on top of oil changes and engine maintenance is more important than ever. A little preventative care goes a long way in keeping these advanced systems running at their best.
📚 Sources:
- Wikipedia contributors. Active Fuel Management. Wikipedia.
- GM Authority. GM Active Fuel Management / Cylinder Deactivation Technology. GM Authority.