Short answer
AFM (Active Fuel Management, from 2005; to 2022.0 on trucks and SUVs, later on the Camaro and Corvette) switches a V8 between 8 and 4 cylinders using 8 special lifters. DFM (Dynamic Fuel Management, 2019+ L84 and L87 only) can shut off any cylinder, runs 17 patterns from 1 to 8 cylinders and uses all 16 lifters. Both can be disabled; DFM on 2022.5+ trucks and 2021+ SUVs needs a dedicated Global B module.
Side by side
| AFM | DFM | |
|---|---|---|
| Years | 2005–2022.0 on trucks/SUVs; Camaro to 2024, Corvette still (V8 and 4.3L V6) | 2019–2026 |
| Engines | LY5, LMG, LC9, LH6, L94, L83, L86, L82, LV3, LT1… | L84 (5.3L) and L87 (6.2L) only |
| Lifters that can switch off | 8 of 16 (4 on the 4.3L V6) | All 16 |
| Modes | V8 or V4 (V6 or V4) | 17 patterns, 1 to 8 cylinders |
| Hardware | Lifter oil manifold with 4 solenoids | 8 individual oil control valves |
| How it feels | Noticeable switch, drone in V4 | More frequent, subtler changes |
| Disabler you need | Classic (OBD-II) | Classic up to 2022.0 with a 6/8-speed; Global B module on 2022.5+ trucks and 2021+ SUVs |
How AFM works
On an AFM V8, cylinders 1, 7, 6 and 4 can go quiet. Each has two special lifters made of two parts held together by a locking pin. When the engine computer decides the load is light, a plate in the engine valley with four solenoids sends oil pressure to those lifters; the pin unlocks, the lifter collapses on itself and the cam no longer opens the valves. Fuel and spark stop on those cylinders and the engine runs as a V4. The saving is usually put at about 5.5 to 7.5% on the EPA test cycle, less in real driving.
How DFM works
DFM, based on Tula Technology's "skip fire" approach, puts a deactivating lifter on every cylinder and an individual oil control valve for each one. The computer recalculates around 80 times a second and can run any of 17 patterns, from one to eight cylinders, fixed or rotating. You feel fewer clunks, but the lifters switch far more often: BOOST, a disabler maker, claims a cylinder can deactivate more than 1,500 times in 15 minutes of driving (maker's figure).
Which engines have which
DFM is only on the 5.3L L84 and 6.2L L87, in Silverado and Sierra 1500 trucks from 2019 and in the Tahoe, Suburban, Yukon and Escalade from 2021. Everything else with cylinder deactivation, including the 2019–2021 base 5.3L L82 and the 4.3L V6, uses AFM. Watch for the YK9 code: many 2021–2022 L82/L84 trucks were built with the system off. Check yours.
Reliability: what's documented
Both systems depend on oil pressure and lifters with moving parts. GM issued technician bulletins (PIP5776 and PIP5861) about misfires from collapsed lifters on 2021–2022 L84 and L87 engines built in specific periods, and a class action over AFM/DFM lifters (Harrison v. General Motors) is still pending. Separately, the 2025 L87 recall (25V-274) concerns crankshaft and rod bearings, not lifters. Lifter failure explained.
What it means when you buy a disabler
- AFM vehicle (2007–2021): any classic plug-in disabler is built for it. Choose on battery draw, switch and reviews.
- DFM truck 2019–2022.0 with a 6- or 8-speed: classic disablers are sold for it.
- DFM truck with the 10-speed (L87, some L84): Range lists its RA003B; most clones exclude it.
- DFM on 2022.5+ trucks or 2021+ SUVs: only Global B modules such as the Range RA007 or BOOST DFM. Our picks.
Questions owners ask
Is DFM more reliable than AFM?
Nobody has published independent failure rates. DFM switches far more often and on all 16 lifters, and GM issued bulletins about collapsed lifters on 2021–2022 L84/L87 engines built in specific periods. AFM engines have their own history of lifter and oil-consumption bulletins.
Can I tell which one I have from the dashboard?
Not reliably. Check the engine code on the glovebox sticker: L84 and L87 are DFM, the others with cylinder deactivation are AFM.
Does the same disabler work on both?
Classic disablers cover AFM and pre-2022 DFM trucks with a 6- or 8-speed. DFM trucks from the 2022 refresh (and 2021+ SUVs) need a Global B module.
Sources
- Jalopnik: how GM AFM/DFM lifters work and fail
- Engine Professional: GM AFM and DFM comparison
- Underhood Service: GM Active vs Dynamic Fuel Management
- GM service bulletin 20-NA-038 (LOMA vs oil control valves)
- GM PIP5776 / PIP5861 (2021–2022 L84/L87 collapsed lifters)