Most product pages hide the biggest drawback in a footnote; we put ours in the title — because the number comes from GM, and you deserve the whole bill.
⏱ The 10-second version
🚫 This trade isn't for you if:
- You bought the truck for its EPA sticker — AFM exists to earn that number, and you'd be handing roughly 1 MPG back
- Your miles are long, steady highway cruises — that's where AFM gets the hours to actually save, so that's where you'd feel the loss most
- You want AFM off for $0 — the M5 method exists, and we wrote the tutorial ourselves
- Your AFM is already off via tune or delete — there's nothing left to unplug
✅ The trade works if:
- You'll swap ~1 MPG for ending the V4 lock/unlock cycling — the one thing this device actually does
- Your driving is mostly stop-and-go, where linked owner reports most often say "little to no change"
- You've read the worst owner number we could find (~1.5 MPG lost) and can live with it
- You want the exit door open — this is a plug, not a reflash
💡 Where the 1 MPG comes from (not from us)
During the 2021 chip shortage, GM built new trucks with AFM/DFM switched off straight from the factory — hardware intact, feature dormant — and put the fuel-economy penalty at about 1 MPG.
GM also gave buyers of those trucks a $50 credit for the missing feature. So the manufacturer's own accountants priced it at fifty bucks. Make of that what you will.
And this wasn't a one-week experiment: the AFM/DFM-less builds ran into the 2022 model year across a documented list of trucks and SUVs. A lot of factory V8-only GM trucks are on the road right now because GM shipped them that way.
So that's the price on the tag. Now the messy part: owner fuel logs scatter in both directions around GM's number — from about 1.5 MPG worse, through no change at all, to one commuter who measured slightly better. Links and caveats below.
The details
The owner numbers: worse, same, better
- Worse: one long-running thread includes a report of roughly 1.5 MPG lost after installing a disabler.
- Same: in a thread asking exactly this question, replies report minute-to-no change — including a 5.3 Tahoe owner a month and a half and a 3,000-mile trip in. A Silverado owner's hand-calculated city average came out identical before and after a full mechanical delete (highway within 0.2 — though he changed other parts at the same time, so file it accordingly). "No change" reports also show up here.
- Better: one commuter toggled AFM off as an experiment and logged 20.1 MPG on a route that normally returns 17.8–18.3 — and, credit to him, immediately flagged weather and fuel blends as possible explanations.
Every one of these is a single truck, a single driver, a single season. Fuel blends change, temperatures change, right feet change. Nobody runs a controlled test on their commute — which is why we lead with GM's number instead of the happiest anecdote.
Why city drivers feel it least (the theory)
AFM saves fuel by holding V4 during light, steady load. A long highway cruise gives it hours of that. Stop-and-go gives it seconds at a time, interrupted by constant V4↔V8 transitions. One owner goes as far as pegging AFM's entire benefit at 0.5–1 MPG of steady-state highway driving — his estimate, not GM's, but it rhymes with GM's ~1 MPG figure.
Meanwhile, those constant transitions are the exact lock/unlock cycling this device exists to remove. So a city-heavy duty cycle is the one where you give up the least fuel and remove the most cycling. Tidy theory, fits the linked reports — and still a theory: GM has never published a city/highway split for AFM's savings, so we won't pretend one exists.
❓ Quick questions
Some owners swear their MPG got better after disabling — especially in town. Real?
The posts are real — the experiment above measured a gain, and city-heavy "no change" reports are common. The theory holds together too: little sustained V4 time in traffic means little savings to lose. But those are anecdotes tangled up with weather, fuel blends and driving habits, and we sell the thing — so we won't promise you a gain. Plan on GM's ~1 MPG. If your fuel log disagrees, enjoy it.
What does 1 MPG cost in actual dollars?
Run your own numbers, but here's the shape of it: 15,000 miles a year at 16 MPG instead of 17 is about 55 extra gallons. At $3.50 a gallon, that's roughly $190 a year — about $16 a month. That's the real price of this device, on top of the sticker. We'd rather you do that multiplication before buying than after.
If I hate the trade, am I stuck with it?
No. It's a plug-in: unplug it and the truck goes back to stock AFM behavior — nothing was reflashed, so there's nothing to undo. And the free M5 method doesn't expire either.
The pitch, with the price tag showing
One breath: you pay about 1 MPG — GM's estimate, not ours — and in exchange the truck stops the V4 lock/unlock cycling, which is the only thing this device does. It repairs nothing. It guarantees nothing. It unplugs back to stock.
If that math works for you: check if it fits your truck →
Not sold? Fair. The M5 method costs nothing — here's our own tutorial.
Sources: the forum threads above are individual owner reports, not fleet data — they're linked so you can judge them yourself. GM's ~1 MPG estimate and the $50 credit come from 2021 chip-shortage coverage by Autoblog and GM Authority; the model-year list is via GM Authority. All links accessed July 2026.
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