What Does AFM Stand For? The Complete Acronym Guide

GlossaryUpdated September 20, 20265 min read

What does AFM stand for? It is an abbreviation for Active Fuel Management which is General Motors' name for cylinder deactivation. It is a system that shuts down four of a V8's eight cylinders during light-load cruising to save fuel.

While this answers the question, the situation often goes beyond that. When you search on any GM truck forum, you will run into DFM, DOD, MDS, VLOM, LOMA and DFCO within a single thread. Although these terms mean slightly different things, people often use them interchangeably in discussions. In this glossary, we will clarify and distinguish them.

AFM — Active Fuel Management

It is GM's current name for its cylinder deactivation system on Gen IV and Gen V small-block V8 engines. It deactivates cylinders 1, 4, 6 and 7 and runs the engine as a V4 mode until more power is required.

Mechanically, it works through lifters that collapse internally when fed pressurised oil, so the camshaft lobe's motion is absorbed inside the lifter instead of opening the valve.

In conclusion, when people mention 'AFM truck', they usually refer to models with a GM V8 from about 2007 to 2018.

DOD — Displacement on Demand

This is the original name used by General Motors (GM) when it first introduced the technology on its 2005 models. For marketing reasons, the system was soon renamed Active Fuel Management, but the old name did not disappear entirely.

In fact, DOD and AFM refer to the same GM system. If you see 'DOD delete kit' and 'AFM delete kit' listed separately, they are almost certainly the same product.

Confusingly, in the aftermarket, 'DOD' is also used as a general term for any cylinder deactivation system, including on non-GM engines.

What Does AFM Stand For Versus DOD?

Although the names are different, the refer to the same GM technology from different eras. AFM is the current term and the one you should use for searches. While DOD is the older term that are found mainly in parts listings and long-running forum threads.

DFM — Dynamic Fuel Management

This is the successor to AFM, which was used on the 2019-and-newer L84 5.3L and L87 6.2L engines.

AFM only switches between eight and four cylinders, while DFM manages seventeen different firing patterns and can run on any number of cylinders. In fact, it adjusts continuously rather than simply switching between two states.

This abbreviation is really important when you shop for parts. A module which is written for AFM logic may not work with a DFM engine, but listings often fail to make the distinction clear.

MDS — Multi-Displacement System

This is Chrysler's equivalent technology, which is applied to the HEMI V8s. It achieves the same basic function by a similar collapsible-lifter approach.

MDS is worth knowing because forum discussions about cylinder deactivation often mix GM and Chrysler owners, but parts are not interchangeable. It means a module sold for a HEMI engine cannot be used on a Silverado.

VLOM and LOMA — The Oil Manifold

VLOM stands for Valve Lifter Oil Manifold, while LOMA stands for Lifter Oil Manifold Assembly. They refer to the same component, which is installed in the engine valley beneath the intake manifold.

Its job is to direct pressurized oil to the four deactivating lifters when the computer commands a switch to V4 mode. It contains an ECU-controlled solenoid valve. Since it must be blocked off when the AFM hardware is removed, it is a common part in AFM delete kits.

If a forum post mentions a VLOM code or a VLOM replacement, it is referring to this part.

DFCO — Deceleration Fuel Cut-Off

It is often confused with AFM, but they are totally different.

DFCO will completely cuts off fuel when you lift off the throttle above a certain RPM such as coasting downhill, or slowing for a light. At this time, the engine is driven by the wheels, so it needs no fuel to keep spinning. Almost all modern fuel-injected engines do this, including engines with no cylinder deactivation whatsoever.

AFM shuts down half the cylinders while you are still applying throttle. Instead, DFCO cuts off the fuel supply to all cylinders while you are not. Therefore, disabling AFM does not disable DFCO, and there is no reason to disable DFCO.

Other Terms Worth Knowing

A 'disabler' is a plug-in OBD-II module that prevents deactivation from engaging without changing anything permanently. A 'delete' is a mechanical job that removes the hardware and a 'tune' is a rewritten ECU calibration. Although these three terms are often used interchangeably in conversation, they actually mean quite different levels of intervention, cost and reversibility.

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Reading a Parts Listing Without Guessing

Once you understand the acronyms, it will be easier to judge the listings, because most of the ambiguity in this market is from terminology rather than the technology itself.

For example, if you see a listing titled 'AFM/DFM disabler' which never specifies a model year, it is making a broad claim it may not support. Also, when you see a listing headed 'DOD delete kit', it is actually selling mechanical parts rather than an electronic module, even though both appear in the same search results. However, a listing that says only 'GM V8' offers no useful information, because GM produces V8s with AFM, with DFM and with neither.

In fact, the truly useful information is always the application list, including specific years, engines and models. Titles are often merely marketing tools, while application lists are claims a seller has to stand behind.

There is one more point worth keeping in mind: a disabler and a delete kit solve the same problem at completely different levels of cost and permanence. If the search keywords are wrong, you might end up with the wrong product category entirely, and the prices can differ by an order of magnitude.

What Does AFM Stand For When Sellers Get It Wrong?

Many product listings use AFM, DOD and DFM interchangeably, and some even use all three in one title cover a wide range of search keywords. That is not necessarily dishonest, but it does mean the title cannot be trusted and cannot tell you what the product actually controls. Therefore, you should read the application list in advance. But if there is no application list, you can just treat the absence as the answer.

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