Semiconductor shortage: GM builds pickups without fuel economy module

I’ve never heard of a fuel economy module! This seems like some kind of scam. What part can be removed that will make the vehicle still pass emissions requirements but get 1MPG worse fuel economy?

A programming chip that would instruct the transmission to upshift sooner under light throttle.

No effect on emissions. It will affect GMs CAFE.

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


So what’s next? Are they going to ship some vehicles without trailer hitch attachment points due to the semiconductor shortage? Or will it be the engine oil dipstick that goes away? Maybe some models will ship without hubcaps on the wheels?

… Or maybe they could ship vehicles without OnStar? Nah we’ll never see that.

Pretty amazing you can save 1 mpg with a chip and have your production influenced. Probably could save more by driver training, Imagine a ticket for jackrabbit starts? Not going to happen.

I bet a lot of people would be happy to see those AFM chips stay away permanently.
Remember GMs first attempt with the 8-6-4 engine?
AFM is far better with modern control, but also far from trouble free.
This scheme didn’t work out so well for Honda either.


I saw this posted on a GM truck forum a year or two ago. People were excited that they could possibly buy a new truck without the cylinder deactivation software. Unfortunately, the hard parts for cylinder deactivation are still in the motor (collapsible lifters, mainly). Lifter failure (usually one or more of the AFM lifters) is one of the main complaints/drawbacks of GM’s AFM system.

I owned an 08 Silverado with AFM. If it worked exactly right, it wasn’t an issue and sort of felt like shifting into another overdrive gear. Unfortunately, at 60k miles or so, mine started to audibly misfire or spark knock when AFM kicked in at low rpm’s. Also, you could hear some lifter noise momentarily on a cold start. I’m not sure what the problem was exactly. Maybe one of the collapsible lifters wasn’t collapsing completely and caused a slight misfire or something. I’ve always been curious. Maybe one of the experts here will chime in and tell me. If I used 93 octane, the noise would go away. Rather than mask the issue with high octane, I replaced the plugs, tried running the engine with no MAF input, and took the truck to 3 dealerships as it was still under warranty.

No help from dealerships or warranty, so I traded it for a new F150, which I traded 17k miles later for my wife’s current Highlander. Probably the worst era of vehicle financial responsibility in my life :joy:. Haven’t bought a new vehicle since then, but I’m due to buy another in the next few years probably.

I had the misfortune to have been driving for a limo firm that owned one Fleetwood Cadillac V-8-6-4 limo, and because I was the rookie, I was frequently assigned to that bomb, which the other drivers avoided like the plague. It was nicknamed the V-8-6-4-2-0 because of its pathetic acceleration at times when you really needed it, and its tendency to stall. :face_with_symbols_over_mouth:

When I complained to the company owner, he told me that I wasn’t “warming it up enough” before driving it. He claimed that–during the summer–it had to be “warmed-up” for at least 30 minutes before driving it. Trust me… that didn’t help.

Luckily, I was able to drive an Olds 98 most of the time, and I really enjoyed that car. But, whenever I drew the short straw and got the Fleetwood limo powered by that inadequately-developed engine, I knew I was going to have a really bad day.

Most manufacturers have some V8 with cylinder deactivation now. Dodge actually employed it on the Hemi in 2005. GM has it, obviously. I think Ford put it on the Coyote in 2020 or 2021 model year. Honda had it (not sure if they still do, and it was on a V6, of course).

The Caddy V8-6-4 engine was ahead of its time… and ahead of the technology to make it work properly and transparently. GM’s air spring suspension from the late 1950s was another example of that. Same for the turbocharged V8 F85 Oldsmobile with water/methanol injection.

I’ve experienced AFM/DoD on both GM and Chrysler V8s. When it works, it is pretty transparent. The Hemi Jeep I drove with it had a snarly exhaust that changed note when the engine switched modes to a rather farty sound. It was the only way I could tell it switched. The technology works…until the parts break.

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Read above comment, this is a win for the consumer, dump the fuel “management “.


As a young man in 1985, my first job in high school was at a corner Chevron station (they all had garages, right?). The owner’s wife drove a beautiful 1981 Eldorado V-8-6-4. I was able to learn a lot watching the senior mechanics work on that car every month or so, trying to keep the car running satisfactorily.

Some time around 1988 the car came in with an odd rattling sound. The guys isolated it to the rear of the engine, removed the torque converter cover, and found a cracked flex plate. The head mechanic was able to finagle a stick welder up in there to tack the crack together and off the car went to be traded on a new Eldorado!

Yeah was going to say the engine will probably last longer without cylinders and coil packs turning on and off all the time .

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So did GM put this feature in a separate module so that users who didn’t like it could remove it, but the truck would still have the higher EPA fuel economy rating?

I say that because there is nothing about cylinder deactivation that would need to be done in a separate module. Is there some kind of mechanical feature in the valves that prevents the valves from opening on a deactivated cylinder? I guess that could need a different module to prove the power to control that if it wasn’t part of the original ECU design.

Boy I got assigned to some bombs when snow plowing, A unimog with the worst stick shift ever, then a garbage truck with a plow, sow with a plow it was called. I had so much fun in a single plow dump truck with a bed full of salt, I loved spinning out the back wheels and making a perfect curb cut on a 15’ radius corner. Then they switched to a plow and wing, not as much fun.

The Powertrain Control Module is different for engines with cylinder deactivation, if the supplier can’t provide these modules, then those trucks won’t be manufactured.

These trucks were available with or without Dynamic Fuel Management and/or Automatic start/stop.


The AFM programming is in the PCM. I’m not exactly sure how the chip shortage comes into play, unless the AFM data is in its own “chip”.

Mechanically, some of the lifters are a two piece design and collapsible. They collapse by oil pressure, which the pcm opens a solenoid or something to direct the oil through certain passages when needed. Lifters collapsed, valves don’t move, computer doesn’t fire coils or injectors, etc. Here is a better explanation:

“So how does the system actually work? In the low load situations, the vehicles computer will send a signal to the engines Lifter Oil Manifold Assembly, which activates solenoids that open allowing oil to flow through special lifters housed within the ADM towers of the engine block. This oil then collapses the plunger inside the lifter, which won’t allow the lifter to engage the push rod, so the valves remain closed for that cylinder. Obviously, with the valves closes, no air can enter or exit that cylinder, meaning it provides no power. When engine load increases, the computer sends the signal back to the lifter oil manifold assembly to close the solenoids, oil bleeds off of the lifters and they return to natural operation and the cylinders begin contributing again”

The only way to turn it off that I’m aware of is aftermarket tuning. It will also default to off (or it did in older models) in tow mode or locking out 6th gear and driving in 5th rather than 6th. The aftermarket sells a device that plugs into the OBD port that shuts it off also.

It’s really not an issue, until you have a mechanical failure (like a fluctuation in oil pressure or the collapsed lifters failing to completely lock when commanded, etc), which is fairly common. There’s some debate whether deactivating the system lessens the chance for mechanical problems, or if the offending hard parts will fail anyway.

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AFM should be in its own chip. If it can be deactivated, then inserting a shorting block where the AFM chip goes would mimic deactivation.

I have a 2009 Dodge with the 5.7L Hemi V8. The MDS system works just fine for me. I’ve gotten up to 26 MPG on the highway with it, in fact.

I can tell when the system kicks on or off, but aside from that it’s pretty transparent. I don’t understand why some folks go to such lengths to disable it.

Search “Active Fuel Management problems” and you will see why many are not a fan of it. Dodge doesn’t seem to have as many issues as GM for whatever reason.

I agree, as long as it’s working correctly, it’s not an issue. I test drove a used Ram Sport with MDS, and I don’t know if they had the wrong oil in it or what, but something was obviously wrong when it dropped to 4 cylinders. Pretty obvious buzz and vibration. My dad’s 2019 Challenger, on the other hand, MDS works seamlessly. I haven’t told him it’s equipped with it and I doubt he’s even aware. Feels similar to shifting into another overdrive. And it’s an 8 speed, so you lose track of which gear it’s in. Similarly, the Ram work truck of a coworker has the 5.7 and MDS works fine at a little over 100k miles.