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Active Fuel Management
Active Fuel Management
Active Fuel Management
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Active Fuel Management (formerly known as displacement on demand (DoD)) is a trademarked name for the automobile variable displacement technology from General Motors. It allows a V6 or V8 engine to "turn off" half of the cylinders under light-load conditions to improve fuel economy. Estimated performance on EPA tests shows a 5.5–7.5% improvement in fuel economy.[1]

GM's Active Fuel Management[2] technology used a solenoid to deactivate the lifters on selected cylinders of a pushrod V-layout engine.

GM used the Active Fuel Management technology on a range of engines including with the GM Small Block Gen IV engine family, first-generation GM EcoTec3 engine family, second-generation GM High-Feature V6 DOHC engine family, and first-generation High-Feature V8 DOHC engine family. Vehicle applications included the 2005 Chevy TrailBlazer EXT, the GMC Envoy XL, Envoy XUV, and Pontiac Grand Prix.

Displacement on demand

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General Motors was the first to modify existing production engines to enable cylinder deactivation, with the introduction of the Cadillac L62 "V8-6-4" in 1981.

Second generation

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In 2004, the electronics side was improved greatly with the introductions of Electronic Throttle Control, electronically controlled transmissions, and transient engine and transmission controls. In addition, computing power was vastly increased. A solenoid control valve assembly integrated into the engine valley cover contains solenoid valves that provide a pressurized oil signal to specially designed hydraulic roller lifters provided by Eaton Corp. and Delphi. These lifters disable and re-enable exhaust and intake valve operation to deactivate and reactivate engine cylinders [1]. Unlike the first generation system, only half of the cylinders can be deactivated. It is notable that the second generation system uses engine oil to hydraulically modulate engine valve function. As a result, the system is dependent upon the quality of the oil in the engine. As anti-foaming agents in engine oil are depleted, air may become entrained or dissolve in the oil, delaying the timing of hydraulic control signals. Similarly engine oil viscosity and cleanliness is a factor. Use of the incorrect oil type, i.e. SAE 10W40 instead of SAE 5W30, or the failure to change the engine oil or oil filter at factory recommended intervals, can also significantly impair system performance.[citation needed]

In 2001, GM showcased the 2002 Cadillac Cien concept car, which featured Northstar XV12 engine with Displacement on Demand. Later that year, GM debuted Opel Signum² concept car in Frankfurt Auto Show, which uses the global XV8 engine with displacement on demand. In 2003, GM unveiled the Cadillac Sixteen concept car at the Detroit Opera House, which featured an XV16 concept engine that can switch between 4, 8, and 16 cylinders.

On April 8, 2003, General Motors announced this technology (now called Active Fuel Management) to be commercially available on 2005 GMC Envoy XL, Envoy XUV and Chevrolet TrailBlazer EXT using optional Vortec 5300 V8 engine. GM also extended the technology on the new High Value LZ8 V6 engine in the Chevrolet Impala and Monte Carlo as well as the 5.3L V8 LS4 engine in the last generation Chevrolet Impala SS, Monte Carlo SS and Pontiac Grand Prix GXP. In both designs, half of the cylinders can be switched off under light loads.

On July 21, 2008, General Motors unveiled the production version of the 2010 Chevrolet Camaro. The Camaro SS with an automatic transmission features the GM L99 engine, a development of the LS3 with Active Fuel Management which allowed it to run on four cylinders during light load conditions.[3]

Third generation

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In January 2018, GM announced an improved version of AFM called Dynamic Fuel Management to be initially released in Chevy Silverado trucks. This system shuts off any number of cylinders in a variety of combinations, maximizing fuel economy and avoiding switching between banks of cylinders.[4][5] This is achieved by using oil pressure solenoids to collapse each individual hydraulic valve lifter, allowing for fully independent individual cylinder control. The system is based on Dynamic Skip Fire,[6] a technology developed by California company Tula Technology.[7] The 6.2L V8 engine of the Chevrolet Silverado incorporating the technology was named one of Ward's 10 Best Engines for 2019.[8]

See also

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References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Active Fuel Management

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from Grokipedia
Active Fuel Management (AFM), also known as Displacement on Demand (DOD), is a deactivation technology developed by (GM) to enhance in internal engines by temporarily disabling a portion of the cylinders during low-load driving conditions, allowing the engine to operate on fewer cylinders without compromising performance. GM first introduced AFM in 2005 on select V8 engines, such as the 5.3L variant in the Gen IV small-block family, with subsequent applications to 6.0L and other engine sizes, marking a significant advancement in engine design aimed at meeting stricter fuel economy regulations. The system was initially branded as Displacement on Demand before being rebranded as Active Fuel Management, and it has since been applied to various V6 and V8 s, including those with RPO codes like LY5, LC9, L76, and L94. Mechanically, AFM relies on an control module (ECM) that monitors conditions; under loads like highway cruising, it signals solenoids in the lifter oil manifold assembly (LOMA) to redirect pressurized oil, causing specialized hydraulic lifters to collapse and prevent actuation on targeted cylinders—typically four out of eight in V8 applications (cylinders 1, 4, 6, and 7), effectively converting the engine to a V4 mode while halting to those cylinders. This reduces pumping losses and fuel consumption, with the system seamlessly reactivating all cylinders when acceleration or higher loads demand full power. The primary benefit of AFM is improved fuel economy, with gains of up to 12% reported in real-world light-load scenarios, helping achieve better miles per gallon without the need for downsized engines or turbocharging. It has been widely implemented in GM's truck and SUV lineup, such as the and GMC Sierra starting from the 2007 , contributing to compliance with (CAFE) standards. In 2018, GM evolved the technology into Dynamic Fuel Management (DFM), which expands flexibility by offering 17 selectable firing patterns to deactivate any combination of cylinders, further optimizing efficiency and reducing vibrations compared to AFM's fixed half-cylinder shutdown. Although introduced in 2019, as of 2025, GM has begun phasing out DFM in some applications due to reliability issues, with discontinuation trends emerging for future models. Despite its advantages, AFM has drawn criticism for reliability concerns, particularly premature wear on AFM-specific lifters due to repeated collapsing and extension cycles, which can lead to ticking noises, increased oil consumption, and in severe cases, catastrophic damage from collapsed lifters or scoring. These issues have been most commonly reported in 2007–2018 GM vehicles with 5.3L or 6.2L V8 engines, prompting many owners to install aftermarket disable kits or tuning devices to prevent activation. DFM, while addressing some of AFM's limitations through smoother operation, continues to use similar lifter technology and may face analogous long-term challenges.

Introduction

Definition and Purpose

Active Fuel Management (AFM) is a trademarked system developed by that deactivates select cylinders in V6 and V8 engines during light-load conditions to reduce fuel consumption while preserving vehicle performance. This technology enables the engine to run on fewer cylinders—such as a V8 operating in V4 mode—seamlessly transitioning back to full displacement when additional power is required. The core purpose of AFM is to improve in internal combustion engines under varying loads, achieving an estimated 5.5–7.5% gain in fuel economy per EPA testing without sacrificing power output or necessitating smaller engines. It was specifically engineered for pushrod V-layout engines to help automakers comply with (CAFE) standards, which mandate higher fleet-wide efficiency to reduce and emissions. At a basic level, AFM operates by using engine oil pressure to control specialized lifters, which deactivate the and exhaust valves on targeted cylinders during low-demand scenarios like steady driving, thereby minimizing use without driver intervention. An early precursor to this system appeared in the Cadillac V8-6-4 engine, marking ' initial foray into cylinder deactivation.

Historical Development

Active Fuel Management (AFM), originally known as cylinder deactivation, traces its origins to the early amid efforts to address escalating fuel demands following the 1970s oil crises. The technology was first implemented in production vehicles with the introduction of Cadillac's L62 V8-6-4 engine in 1981, marking the debut of a system capable of seamlessly switching between 8-, 6-, and 4-cylinder operation to optimize under varying loads. This innovation was directly influenced by the establishment of U.S. (CAFE) standards in 1975, which aimed to enhance vehicle efficiency and reduce reliance on imported oil in response to global energy shortages. Despite its pioneering status, the early V8-6-4 system encountered significant reliability challenges during the , including rough transitions between cylinder modes that caused engine bucking, shaking, and customer dissatisfaction. These issues, compounded by the limitations of contemporary electronics and components, led to widespread complaints and service demands, prompting to discontinue the technology after just the model year. Throughout the and 1990s, deactivation remained dormant in production applications due to these unresolved drivability and durability concerns, though research continued in parallel with tightening CAFE requirements and emissions regulations. The technology experienced a revival in the early 2000s, rebranded as Displacement on Demand (DOD) and refined with advanced electronics for smoother operation. A key milestone came in 2004, when GM detailed enhancements in control systems, enabling more reliable cylinder deactivation without compromising performance. DOD was relaunched in production for the 2005 model year, initially applied to the 5.3-liter in midsize SUVs like the Chevrolet TrailBlazer, expanding to a broader range of GM vehicles thereafter. This iteration addressed prior shortcomings, delivering fuel economy improvements of 5-7.5% under light-load conditions while meeting evolving CAFE mandates. Further evolution occurred in 2018, when GM announced Dynamic Fuel Management (DFM) as a sophisticated advancement over DOD and AFM, allowing deactivation of any combination of cylinders in up to 17 patterns for even greater efficiency and seamless power delivery. As of 2025, DFM remains in production across various GM V8 engines, contributing to ongoing fuel efficiency efforts amid stricter emissions regulations. This development continued the trajectory shaped by regulatory pressures, including updated CAFE standards, positioning AFM as a cornerstone of modern fuel-saving strategies in internal combustion engines.

Technical Principles

Cylinder Deactivation Mechanism

Active Fuel Management (AFM) achieves cylinder deactivation through a hydraulic system that prevents valve operation in selected cylinders without altering the engine's mechanical structure. Specially designed hydraulic roller lifters, one for each intake and exhaust valve on the cylinders to be deactivated, incorporate a spring-loaded locking pin that maintains normal valve actuation under full-load conditions. When deactivation is commanded, pressurized engine oil flows into the lifter, releasing the locking pin and allowing the outer shell of the lifter to collapse relative to the inner plunger, thereby holding the valves closed and preventing air intake or exhaust while the piston continues to reciprocate. Solenoid valves, typically four in number for a V8 engine and mounted in the valve lifter oil manifold (VLOM), control this process by directing oil to the specific lifters corresponding to cylinders 1, 4, 6, and 7. The system relies on engine oil pressure, generated by the oil pump and typically ranging from 20 to 40 psi during operation (with a minimum of 22 psi required for reliable lifter at hot idle around 25 psi), to route through screened passages in the VLOM and into the lifters. When solenoids energize, high-pressure oil unlocks the lifters, enabling collapse; in deactivated mode, the pistons compress and expand rather than an air- mixture, minimizing pumping losses. injectors and ignition for these cylinders are simultaneously disabled to avoid . The electronic control module briefly oversees actuation to ensure synchronized deactivation. To maintain engine balance and smoothness, the adjusts the and fuel delivery, skipping the deactivated cylinders (1, 4, 6, and 7) while firing the active ones (2, 3, 5, and 8) in the standard sequence of 1-8-7-2-6-5-4-3, effectively operating as a balanced V4. This reconfiguration occurs seamlessly during transitions, completing the shift to or from deactivation mode in less than 20 milliseconds—encompassing solenoid response and lifter hydraulic adjustment—typically under light-load conditions such as less than 6% angle and steady highway cruising. AFM is primarily compatible with pushrod overhead (OHV) V8 engines, such as GM's LS-series, and also in select V6 engines with analogous deactivation of two cylinders, where the architecture supports the additional VLOM and oil passages without major redesign. Implementation requires profiles optimized for the collapsible lifters, featuring appropriate lobe durations and lifts to accommodate the lost motion during deactivation, along with springs capable of handling the altered dynamics while preventing float.

Control Systems and Sensors

The (ECU), also known as the Engine Control Module (ECM) in GM applications, serves as the central processor for Active Fuel Management (AFM), analyzing from various sensors to determine optimal cylinder activation or deactivation. It employs algorithms that evaluate engine load, speed, and temperature to initiate AFM mode, ensuring seamless transitions while maintaining drivability. For instance, the ECU commands solenoids within the Valve Lifter Oil Manifold (VLOM) to direct pressurized oil to specific lifters, effectively deactivating selected cylinders under suitable conditions. Key sensors provide the ECU with critical inputs for decision-making. The throttle position sensor (TPS) monitors throttle opening to assess airflow demands, while the manifold absolute pressure (MAP) sensor measures intake manifold pressure to gauge engine load. Crankshaft position sensors track engine speed and position for precise timing of deactivation events, and the coolant temperature sensor ensures activation only when the engine has reached operating temperature to avoid thermal imbalances. Additionally, the accelerator pedal position sensor detects driver input, signaling increases in torque demand that may require full-cylinder operation. AFM activation typically occurs during steady-state highway cruising at speeds between 40 and 80 mph with low demands, such as light on flat , where fuel economy benefits are maximized without compromising performance. The ECU disengages AFM instantly upon detecting via pedal input or increased load, reverting to full-cylinder mode in under 20 milliseconds to maintain responsiveness. These criteria are derived from sensor data thresholds, including stable vehicle speed and RPM, ensuring deactivation only when conditions support balanced operation. Feedback loops enhance system reliability through continuous monitoring. Knock sensors detect potential detonation in active cylinders, allowing the ECU to adjust timing or abort deactivation if imbalances arise. Oxygen sensors maintain air-fuel ratios by providing exhaust data, preventing lean conditions during mode transitions. The oil pressure sensor verifies hydraulic integrity by confirming sufficient pressure (typically 27-66 psi) in the VLOM passages, inhibiting AFM if levels drop to protect lifter mechanisms. AFM integrates with (ETC) and (VVT) to ensure smooth operation across modes. ETC adjusts throttle position dynamically to compensate for reduced displacement, minimizing fluctuations during activation or deactivation. VVT systems, such as cam phasers on and exhaust , optimize timing to reduce vibration and noise, coordinating with ECU commands for balanced firing orders. This synergy allows AFM to operate transparently, with hydraulic lifter adjustments supporting the overall control strategy.

Generations of Implementation

First Generation: Displacement on Demand

The first generation of Active Fuel Management, originally branded as Displacement on Demand (DOD), was introduced by for the 2005 model year as a revival of cylinder deactivation concepts first explored in the company's 1981 V8-6-4 engine. This system marked the initial modern production implementation of technology in GM vehicles, focusing on improving under light-load conditions by seamlessly deactivating cylinders without driver intervention. Key features of this generation centered on a fixed deactivation pattern that shut down exactly half of the cylinders in V8 engines, effectively operating as a V4 during low-demand scenarios such as highway cruising. The mechanism employed basic hydraulic lifter deactivation controlled by four solenoids housed in the Lifter Oil Manifold Assembly (LOMA), which redirected pressurized engine oil to collapse the lifters on the non-firing cylinders, preventing and exhaust operation while the pistons continued to move. The (ECU) managed these transitions using predefined patterns based on throttle position, vehicle speed, and load, with activation typically occurring above 25-40 mph and deactivation under heavier acceleration. Technically, the system was integrated into select Vortec V8 engines, primarily the 5.3L LH6 (producing 290 horsepower and 325 lb-ft of torque) and later the 6.0L LY6 variants introduced in 2007, requiring SAE 5W-30 viscosity oil meeting GM Standard 6094M to maintain adequate hydraulic pressure for reliable operation and lifter function. Synthetic formulations were emphasized for optimal performance, as conventional oils could lead to insufficient pressure and potential deactivation failures under varying temperatures. Early applications debuted in the 2005 Chevrolet TrailBlazer EXT and and XUV SUVs equipped with the 5.3L engine, marking the technology's consumer introduction in mid-size vehicles. The system later expanded to full-size trucks, including the 2007 and GMC Sierra with 5.3L and 6.0L options, broadening its use across GM's light-duty truck lineup. Despite its innovations, the first-generation design exhibited limitations inherent to its binary on/off switching, which could result in noticeable engine vibrations or harshness during mode transitions in some vehicles, particularly if engine mounts or balance shafts were not optimally tuned. The fixed four-cylinder deactivation pattern lacked variability, restricting adaptability to diverse driving conditions and contributing to occasional drivability complaints. Overall, it delivered general fuel economy gains of 5-7% in truck applications under typical use.

Second Generation

The second generation of Active Fuel Management (AFM), introduced by between 2007 and 2010, represented a refinement of the original Displacement on Demand system debuted in 2005, incorporating advanced electronic controls for smoother operation and expanded applicability across engine types. This iteration focused on minimizing perceptible transitions between full-cylinder and deactivated modes, primarily through integration with (ETC), which modulated airflow more precisely to maintain vehicle performance and driver comfort during cylinder deactivation. Upgraded solenoids in the valve lifter oil manifold assembly enabled quicker hydraulic pressure shifts, reducing overall transition times to support seamless mode changes under varying loads. Engine compatibility broadened significantly in this generation, extending beyond initial V8 applications to include select V6 configurations and additional variants of the Gen IV small-block V8 family. For instance, the 6.2L L99 V8, featuring AFM, powered the 2010 SS, allowing the high-performance model to achieve improved efficiency without sacrificing output. V6 support was added to engines like the 3.6L LLT in the 2009 , where deactivation targeted three cylinders (typically 1, 4, and 5) during low-demand conditions to enhance fuel savings in family-oriented SUVs. Notable truck applications included the 2007-2013 1500 with the 5.3L V8, broadening AFM's reach in heavy-duty segments. To address inherent challenges like torque fluctuations from uneven firing orders in deactivation mode, engineers implemented tuned mounts with enhanced characteristics, which absorbed vibrations more effectively and reduced cabin during V4 or V6 operation. System reliability was also influenced by oil specifications; AFM performance depended on proper , with non-synthetic or incorrect formulations (e.g., lacking sufficient anti-wear additives) contributing to lifter failures by promoting buildup and inadequate in the deformable lifter mechanisms. In controlled tests, this generation delivered up to 12% fuel economy improvements, with real-world gains typically ranging from 5-7.5% in applications under light-load conditions.

Third Generation: Dynamic Fuel Management

In January 2018, General Motors announced Dynamic Fuel Management (DFM) as an advanced evolution of its cylinder deactivation technology, debuting on the 2019 Chevrolet Silverado 1500 full-size pickup truck. This system builds on GM's partnership with Tula Technology, incorporating the latter's Dynamic Skip-Fire (DSF) strategy, which GM Ventures had supported since 2012 to enhance fuel efficiency in gasoline engines. DFM represents a shift from earlier fixed-pattern deactivation by enabling more granular control over engine operation, prioritizing seamless power delivery alongside efficiency gains. The core innovation of DFM lies in its ability to deactivate any combination of cylinders in real time, allowing V8 engines to operate across up to 17 distinct firing patterns rather than limiting deactivation to fixed groups like the four cylinders in prior systems. This flexibility, achieved through individual solenoid valves in the engine valley that control oil flow to hydraulic lifters, minimizes vibrations and transitions more smoothly between firing modes, even down to a single-cylinder operation under light loads. The (ECU) continuously monitors driving conditions via sensors to select the optimal pattern, optimizing and reducing fuel use without perceptible performance loss. DFM first appeared on the EcoTec3 family of V8 engines, specifically the 5.3-liter L84 and 6.2-liter L87 variants powering the 2019 Silverado, where it integrates with advanced transmission systems for enhanced overall efficiency. The 6.2-liter version pairs with a 10-speed to further refine shift logic and load management, while the 5.3-liter uses an eight-speed unit. Independent validation came swiftly, with the 6.2-liter EcoTec3 V8 earning a spot on list for 2019 due to its refined power and efficiency. Relative to non-deactivation baselines, DFM delivers fuel economy improvements of up to 15 percent, derived from DSF's foundational testing, though real-world gains vary by . As of 2025, DFM continues to be implemented in GM's EcoTec3 V8 engines for trucks and SUVs, including the 2025 1500. To maintain reliability, DFM-equipped engines require dexos1-approved 0W-20 , with GM recommending changes every 7,500 miles under normal conditions but more frequent intervals—such as 3,000 to 5,000 miles—for severe duty or to mitigate potential lifter wear from variable deactivation. High-quality oil ensures proper hydraulic function in the lifters, preventing issues associated with inconsistent pressure during mode switches.

Vehicle Applications

Affected Engine Families

Active Fuel Management (AFM) has been implemented primarily in ' Vortec and EcoTec3 small-block families, including the 5.3L L83 and L84 variants, the 6.0L L96, and the 6.2L L87 and L8T engines. Limited application extends to certain later V6 engines with compatible DOHC designs, such as the 3.6L LGX High Feature V6 starting in 2018. These engines utilize pushrod overhead (OHV) configurations equipped with hydraulic roller lifters, which enable the deactivation of cylinders by holding lifters in place via oil pressure solenoids; overhead cam (OHC) engines are generally incompatible due to the increased complexity of their systems. The evolution of AFM compatibility reflects advancements in engine architecture: first-generation implementations were restricted to Gen IV small-block V8s, such as the 5.3L LH6, introduced around for improved efficiency in light-load conditions. Third-generation systems, including Dynamic Fuel Management, are featured on EcoTec3 engines with direct injection and specialized cylinder deactivation-ready cylinder heads, allowing more flexible deactivation patterns. Diesel engines like the Duramax series and high-performance variants such as the supercharged LT4 are typically excluded from AFM due to their distinct operational demands and lack of compatible deactivation hardware. Affected engines span displacements from 5.3L to 7.0L, predominantly in and applications where V8-to-V4 operation contributes to fuel savings of up to 7% under cruising conditions.

First Generation: Displacement on Demand (2005-2007)

The initial implementation of Active Fuel Management under the name Displacement on Demand debuted in 2005 on select mid-size SUVs equipped with the 5.3L . This generation focused on basic cylinder deactivation for four cylinders during light-load conditions to improve . Key models included:
  • Chevrolet TrailBlazer EXT (2005-2006), the first to feature the technology.
  • GMC XL (2005-2006), the extended-wheelbase variant of the Envoy lineup.
  • GMC Envoy XUV (2005), a unibody crossover version.
  • (2007), marking the entry of the technology into luxury full-size SUVs.

Second Generation: Active Fuel Management (2007-2018)

The second generation, rebranded as , expanded to a broader range of full-size trucks, SUVs, and performance vehicles, incorporating refined control logic for smoother transitions between four- and eight-cylinder operation. This version was applied to various V8 engines, including the 5.3L and 6.0L variants, across GM's North American lineup from 2007 onward. Notable models encompassed:
  • Chevrolet Silverado 1500 (2007-2013), introducing AFM to light-duty pickups.
  • Chevrolet Tahoe (2007-2014), a full-size SUV with the 5.3L V8.
  • Chevrolet Camaro SS (2010-2015), applying the system to the high-performance 6.2L V8.
  • Chevrolet Suburban (2007-2014), the extended-length SUV counterpart to the Tahoe.
  • Chevrolet Avalanche (2007-2013), a unique crew cab pickup-SUV hybrid.
  • GMC Sierra 1500 (2007-2013), the premium sibling to the Silverado.
  • GMC Yukon (2007-2014), the upscale version of the Tahoe.
  • Pontiac G8 (2009), a rear-wheel-drive sedan with the 6.0L V8.
  • Cadillac Escalade (2007-2014), continuing from the first generation with enhanced V8 options.

Third Generation: Dynamic Fuel Management (2019-Present)

Introduced in 2019, Dynamic Fuel Management advanced the technology by allowing deactivation of any combination of cylinders in 17 patterns, providing more granular control for efficiency and performance. This generation primarily targets EcoTec3 V8 engines in full-size vehicles, with applications expanding to SUVs by 2021, and continues in 2025 models following full reinstatement after temporary removal during the 2021-2022 . Affected models include:
  • Chevrolet Silverado 1500 (2019-2025), standard on 5.3L and 6.2L V8 engines.
  • (2021-2025), integrated into the redesigned full-size .
  • (2021-2025), the long-wheelbase variant with V8 powertrains.
  • GMC Sierra 1500 (2019-2025), mirroring the Silverado's implementation.
  • GMC Yukon (2021-2025), the luxury equivalent to the Tahoe.
  • (2021-2025), featuring DFM on its 6.2L V8.
During the supply chain disruptions, particularly the global semiconductor chip shortage, GM temporarily removed DFM from certain 2021-2022 models equipped with the 5.3L L84 , such as select 1500, GMC Sierra 1500, and heavy-duty variants like the Silverado HD, to maintain production. These vehicles, identifiable by the RPO code YK9, operated in full-cylinder mode without deactivation capabilities. The feature was reinstated across the lineup starting with the 2023 model year as supply chains stabilized.

Global Variants

Active Fuel Management was primarily deployed in North American GM vehicles, with limited adoption elsewhere. In , applied the technology to V8 automatic models of the Commodore sedan and wagon from 2009 to 2017, including the VE and VF generations with the 6.0L L76 and L77 engines, as part of its Ecoline fuel-efficiency initiatives.

Performance and Efficiency

Fuel Economy Improvements

Active Fuel Management (AFM) typically delivers EPA-estimated fuel economy improvements of 5.5% to 7.5% overall for equipped V8 engines under standard testing conditions. For instance, the 2005 1500 with the 5.3L V8 and AFM saw city/highway ratings of approximately 15/21 , with GM claiming up to 20% gains on highway cycles compared to non-AFM predecessors. These enhancements stem from deactivating four cylinders during low-demand operation, reducing fuel use while maintaining V8 performance on demand. Dynamic Fuel Management (DFM), introduced in third-generation systems, achieves up to 5% efficiency gains over non-deactivation V8 configurations in GM trucks. In the 2019 1500, the 6.2L V8 with DFM is rated at 15 city/20 highway for certain configurations, compared to 15/21 for the 2018 non-DFM equivalent, showing similar overall efficiency with potential benefits in mixed driving depending on conditions. As of 2025, recent models like the continue to use DFM with EPA ratings remaining stable around 15/20 for the 6.2L V8, without reported significant further improvements. Fuel economy benefits are assessed through EPA cycle testing, which simulates light-load scenarios comprising 40-60% of typical operation, such as steady cruising. Real-world results can vary based on factors like quality, as AFM relies on precise hydraulic actuation; suboptimal or may reduce deactivation frequency and efficiency. Compared to non-AFM GM V8 engines, AFM adds 1-2 in both city and highway ratings, aiding compliance with (CAFE) standards by boosting fleet-wide efficiency without major redesigns. However, gains diminish to under 5% in stop-go urban traffic or towing scenarios, where high loads prevent cylinder deactivation and full V8 operation is required.

Emissions and Environmental Impact

Active Fuel Management (AFM) primarily reduces (CO2) emissions through its fuel-saving mechanism, achieving approximately 5.5-7.5% improvement in fuel economy on applicable engines, which directly translates to proportional CO2 cuts via lower fuel . During cylinder deactivation, the remaining active cylinders operate at higher loads with stoichiometric air-fuel mixtures, promoting more complete and thereby reducing hydrocarbons (HC) and oxides () emissions compared to full-displacement modes under similar conditions. This improved efficiency on active cylinders minimizes unburned fuel output, contributing to overall lower tailpipe pollutants when integrated with exhaust aftertreatment systems. AFM aids regulatory compliance by enhancing engine efficiency, enabling vehicles to meet stringent U.S. Environmental Protection Agency (EPA) standards such as Tier 2 Bin 5 and later iterations, which limit to 0.07 g/mi and non-methane organic gases (NMOG) to 0.09 g/mi. The technology optimizes exhaust gas temperatures and flow, improving the performance of catalytic converters and allowing for more effective conversion of CO, HC, and into less harmful substances like CO2, , and . From a lifecycle perspective, AFM decreases overall consumption by curtailing use across the vehicle's operational life, though it introduces a minor increase in engine oil consumption due to the hydraulic pumping required for lifter deactivation. Studies, including SAE Technical Paper 2007-01-1292, confirm approximately 5-7.5% CO2 reduction in tested GM 3.9L V6 applications with displacement on demand, highlighting its role in mitigating broader fleet emissions. However, if deactivation transitions are not precisely tuned, incomplete during mode switches can elevate particulate matter emissions temporarily.

Criticisms and Reliability Issues

Common Problems

One of the most prevalent issues with Active Fuel Management (AFM) systems is the failure of hydraulic lifters, particularly in 2014-2021 models equipped with 5.3L and 6.2L V8 engines. These lifters can collapse or become stuck due to oil aeration, debris contamination, or internal locking pin damage from inadequate oil pressure, resulting in cylinder misfires, rough idling, and potential engine damage. Repairing such failures typically involves replacing the affected lifters, camshaft, and related components, with costs often exceeding $3,000, including labor and parts. Vibration and noise problems are common during mode transitions in first- and second-generation AFM implementations, where the engine switches between full-cylinder and deactivated modes, often exacerbated by worn engine or transmission mounts. These issues manifest as noticeable shudders or rattles, particularly at low RPMs around 1,200-1,400 during V4 operation under light load. Third-generation Dynamic Fuel Management (DFM) aims to mitigate vibrations through more varied cylinder deactivation patterns compared to AFM's fixed approach, though some drivers report residual shudders in certain conditions. Increased consumption is another frequent complaint in AFM-equipped engines, with some using up to 1 per 1,000 miles, which GM has described as acceptable in certain high-load or performance contexts, though the standard guideline is 1 per 2,000 miles. This usage may be linked to oil circulation in deactivated cylinders, potentially leading to and buildup without . Electronic control unit (ECU) glitches, often involving faulty AFM solenoids, can trigger check-engine lights and diagnostic trouble codes related to misfires or deactivation faults, particularly in 2007-2013 trucks. These solenoids regulate oil flow to the lifters for cylinder deactivation, and their failure disrupts the process, causing inconsistent performance and illumination of warning lights. NHTSA complaints regarding AFM-related issues, including lifter failures and engine performance problems, have been prominent in models from 2014-2021, with reports highlighting reliability concerns in high-volume trucks and SUVs. A class action lawsuit filed in 2021 (Harrison et al. v. LLC) alleges defective AFM and DFM valvetrain systems causing premature lifter failures in vehicles with 5.3L, 6.0L, and 6.2L V8 engines from 2014-2021, claiming GM concealed the defects. In 2025, issued a for defects in 6.2L V8 s affecting approximately 721,000 vehicles (model years 2021-2024), primarily due to flaws in and components that could lead to failure; this is distinct from AFM/DFM issues. As of October 2025, NHTSA expanded an investigation (EA25007) into potential bearing failures in these L87 s, now covering up to 1.16 million vehicles from 2019-2024, including additional Silverado and Sierra models.

Disabling and Aftermarket Solutions

Owners of vehicles equipped with Active Fuel Management (AFM) or Dynamic Fuel Management (DFM) often opt to disable these systems to address concerns over drivability and long-term health. One primary method involves ECU reprogramming using tools like HP Tuners software, which modifies the control parameters to lock the engine in full-cylinder operation mode via a simple enable/disable toggle in the VCM Editor under Fuel > Lean/Fuel-Saving > DOD settings. This tuning approach is reversible but requires specialized equipment and technical knowledge to flash the ECU. For vehicles from 2019 onward featuring DFM, plug-in modules such as the Range Technology RA003 (for AFM/DFM) and RA007 (specifically for refreshed DFM systems) offer a user-friendly alternative by connecting to the OBD-II port and intercepting signals to prevent cylinder deactivation and auto start-stop activation, maintaining full V8 performance without permanent alterations. These modules are compatible with GM models spanning 2007 to 2025, including popular trucks and SUVs with 5.3L and 6.2L engines. A more comprehensive hardware-based solution entails replacing AFM-specific components with non-AFM equivalents, such as standard camshafts, lifters, and valley cover, to eliminate the deactivation solenoids entirely and ensure the engine operates solely in full-cylinder mode. For Gen V L83 engines, AFM/DOD delete kits from manufacturers such as Scoggin-Dickey, Texas Speed, or LSXceleration replace Active Fuel Management lifters, trays, valley cover, and related components with non-AFM parts, often paired with non-AFM lifters and plugs for AFM towers. These kits eliminate common lifter failures, improve oiling, allow full-time V8 operation, and add 5-15 hp from consistent cylinder firing; they also enable bigger cams and better tuning. A custom ECU tune is required to disable AFM in software. This modification, often performed during routine maintenance or repair, typically costs approximately $2,000, encompassing parts priced around $300 and labor of about $1,000 to $1,700 depending on the shop and location. Disabling AFM or DFM enhances reliability by minimizing the risk of lifter failures linked to cylinder deactivation cycles and delivers more consistent power output and smoother response, particularly beneficial for and . Many owners report that disabling these systems also substantially reduces oil consumption, particularly in higher-mileage engines such as the 5.3L in Chevrolet Silverado trucks, attributing the improvement to fewer deactivation cycles that may exacerbate oil burning; results vary depending on existing engine wear and maintenance. However, these modifications can lead to a minor fuel economy penalty of 1-2 due to the absence of partial-cylinder operation under light loads, though some users report negligible changes or even slight improvements in real-world mixed . ECU tuning generally voids the factory warranty, whereas removable plug-in devices like those from Range Technology are engineered to avoid detection and preserve warranty coverage when uninstalled prior to service. Such disabling solutions have gained significant traction among GM truck owners, especially for 2022 and later models, where automotive forums indicate widespread adoption—often exceeding 50% among those reporting hesitation or mode-switching issues—to achieve a more engaging V8 experience. Legally, aftermarket disablers and hardware fixes remain compliant with federal EPA regulations provided they do not elevate emissions beyond certified levels, aligning with the EPA's Tampering updated on November 23, 2020; however, they are not authorized in or other states following CARB standards without approval. Availability of these options extends across 2007-2025 GM vehicles, with manufacturers like Range Technology explicitly designing products to meet these criteria.

Recent Developments and Phase-Out

Updates Post-2019

Since the introduction of Dynamic Fuel Management (DFM) in 2019, has expanded its application to additional vehicle lines, including the 2021 and full-size SUVs, where it is integrated into the 5.3L and 6.2L EcoTec3 V8 engines to optimize under varying loads. These expansions leverage DFM's ability to deactivate up to seven cylinders in 17 distinct patterns, building on the third-generation system's variable deactivation approach for smoother transitions. During the global supply chain disruptions caused by , GM temporarily removed DFM from certain 5.3L L84-equipped models in the 2021-2022 s due to semiconductor shortages, affecting trucks and SUVs in the lineup. By the 2023 , GM reinstated DFM across the affected 5.3L V8 variants in light-duty trucks like the 1500 and GMC Sierra 1500, restoring the technology's efficiency benefits without hardware changes. GM's partnership with Tula Technology for Dynamic Skip-Fire (DSF) licensing, which underpins DFM, has continued beyond 2019, enabling ongoing refinements in cylinder deactivation control for EcoTec3 engines in trucks and SUVs. To address reliability concerns such as lifter wear associated with DFM operation, GM introduced the dexos1 Gen 3 oil specification in 2021, emphasizing enhanced anti-wear additives and compatibility with V8 engines to reduce friction in deactivation modes. In performance testing, the 2025 Chevrolet Silverado 1500 with the 6.2L EcoTec3 V8 and DFM achieves EPA-estimated ratings of 16 mpg city and 21 mpg highway in 2WD configurations, demonstrating sustained efficiency gains from the system's dynamic cylinder management. General Motors temporarily suspended Dynamic Fuel Management (DFM) in select vehicle lineups starting in 2021 due to supply chain constraints during the . Between March 2021 and the end of the 2022 model year, GM removed DFM—and by extension, auto stop-start—from certain trucks and SUVs, including some 1500 models equipped with the 5.3L V8, to address semiconductor shortages that prevented installation of the necessary control modules. For instance, the 3.0L Duramax in the 2022 Silverado lineup does not incorporate AFM or DFM, as these technologies are designed for gasoline engines and are absent in diesel configurations. This temporary suspension was driven by logistical challenges and ongoing reliability concerns. Persistent complaints about lifter failures linked to AFM/DFM systems, where collapsed lifters lead to engine misfires and costly repairs, have eroded consumer confidence and prompted regulatory scrutiny. disruptions, particularly the global , accelerated the omission of these features in 2021-2022 builds to maintain production volumes. Concurrently, GM's commitment to a zero-emissions future, including a goal to phase out sales for light-duty vehicles by 2035, has shifted resources toward battery-electric vehicles (BEVs) and reduced investment in cylinder deactivation technologies. As of 2025, AFM/DFM remains in select V8 engines, such as the 5.3L L84 and 6.2L L87 in the Silverado 1500, where it continues to enable variable operation for . However, it is omitted from heavy-duty trucks like the Silverado 2500HD and 3500HD, which use the 6.6L V8 gasoline engine without deactivation, and from smaller SUVs such as the , which employs a 1.5L turbocharged inline-four without these systems. A 2025 recall (NHTSA 25V-274) for 2021-2024 models with the 6.2L V8 addresses potential bearing failures due to manufacturing defects that could cause engine damage; the recall excludes 2025 vehicles due to updated components. Reports indicate that the redesigned V8 engines for the 2026 and GMC Sierra will eliminate AFM/DFM to improve reliability. In response, GM has pivoted to alternative powertrains that avoid traditional V8 deactivation mechanisms. The 2.7L TurboMax inline-four, standard in base Silverado 1500 trims, incorporates its own form of deactivation but has fewer reported issues than V8 systems, offering a and efficiency without the lifter complexities of AFM/DFM. Duramax diesel engines, such as the 3.0L in the Silverado 1500, operate without any deactivation, providing robust for while sidestepping gasoline-specific fuel management challenges. Aftermarket disablers remain popular for owners retaining AFM/DFM-equipped V8s, bridging the gap until full transitions occur. Looking ahead, AFM/DFM faces likely full discontinuation by 2030 as GM accelerates BEV adoption to meet its 2035 zero-tailpipe-emissions target for new light-duty vehicles. While legacy internal combustion engines will receive ongoing parts support, the company's investments in electric platforms like the system signal a broader exit from fuel management innovations tied to fossil fuels.

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