AFM Experience

[diyer2]

I've been wrenching on GM trucks for 17 years. And I need to get something off my chest because it's been weighing on me for a long time.

After all that time, all those motors, all those people standing in my bay, I've figured out there are really only two kinds of owners.

The ones who already know about this. And the ones who are about to find out the hard way.

A guy came into my shop a few weeks back in a 2018 Silverado 5.3. Sharp guy, maybe 35. Knew his truck cold. He'd been on the forums, read the threads, done his homework.

He only rolled in so I could double-check a little module he'd already plugged in himself. Wanted a second set of eyes on it. Ten minutes, in and out, drove off happy.

Two days later, a completely different story walked through the same door.

Older fella this time, in a 2016 Sierra. Gorgeous truck, clearly babied, not a scratch on it. Wedding ring. Looked like a guy who took care of his stuff.

He was in because his engine had started knocking on the way to work. And by the time I got the valve cover off, I already knew it was too late.

Lifter collapsed. Cylinder 5. Camshaft chewed up. The whole top end shot.

Same kind of truck. Same motor. Same roads, probably the same dealer. The only thing separating those two men was information.

I've been at this since 2008, and I've worked on everything GM puts out. Silverados. Sierras. Tahoes. Yukons. Suburbans. Escalades. The 5.3 and the 6.2. Doesn't matter which badge is on the tailgate. They all carry the same problem.

So here's the information one of those guys had and the other one didn't.

It's called Active Fuel Management. AFM. GM started building it into their V6s and V8s back in 2007 to squeeze out a little better mileage on the highway. Maybe a mile or two a gallon. All to hit government fuel economy numbers.

The way it works, the motor quietly shuts down half its cylinders when you're just cruising along. And the little lifters that pull that off have a tiny pin inside them that's constantly clicking in and out. Lock, unlock, lock, unlock. Hundreds of times a drive. Thousands of times a week.

Eventually one of those pins wears through. The lifter drops. And it starts grinding the camshaft down like a chisel on butter.

And what nobody tells you is that the shudder you feel around 40 or 50 mph? That's the system cycling. Every single time.

Here's what really gets me. The pre-2007 trucks, the ones without AFM, they're bulletproof. I've got customers still daily driving them with 260,000 miles on the odometer. Not a problem in the world.

GM took a perfectly good motor that would have lasted a lifetime and bolted this system onto it. And it is wrecking engines that should have run forever.

The guys who hang around the forums already know all of this. So do the techs. They handled this years ago. They didn't sit around waiting for the dealership to mail them a warning letter, because that letter is never coming.

It's the guys who figured somebody would've told them who end up on my lift.

And I want to be clear, because this part matters. Maintenance has nothing to do with it. I've torn down motors with barely 30,000 miles on the clock. I pulled apart a Tahoe last summer with 24,000 on it. Practically a brand new truck. Owner had it less than a year.

Spotless oil. Best synthetic money can buy, changed early every time. Made no difference. I've seen guys with full dealer records, every interval stamped. Made no difference.

The oil changes were never the problem. The pin was. And no amount of babying that truck stops that pin from cycling every single time you drive.

That's the part that eats at me. These are good motors. Take the AFM out of the equation and a 5.3 or a 6.2 will run 300,000 miles and never blink.

So a few years ago I started telling every single owner who comes through my doors the exact same thing the smart guys already knew. Get yourself a FullForce disabler.

It plugs right into the port under your dash. Couple of seconds and you're done. It just tells the computer to leave every cylinder running, full time.

No more cycling. No more beating those lifters back and forth every time you turn the key.

It doesn't reprogram anything. Doesn't touch your tune. And unplug it before a dealer visit and there's absolutely zero trace it was ever installed.

I've had customers come back at 40,000, 60,000, 80,000 miles after I put one in. Zero issues. The trucks run smoother. And the lifters aren't getting beaten to death every single drive.

I won't sit here and tell you it's magic. A lifter that's already damaged is a lifter that's already damaged, and this won't un-ring that bell. But it takes away the one thing causing all that wear in the first place. That's the whole game.

You don't need a five-thousand-dollar delete. You don't need an expensive tune. You don't need to tear anything apart. You just need to stop the cycling.

I'm not writing this for any company. I'm writing it because I'm tired of watching the guys who didn't know pay four and five figures for it.

I'm tired of being the guy who has to break the news.

I'm tired of knowing that the guys who did know fixed the whole thing for the price of a tank of gas, and the only difference was that somebody told them first.

If you drive a Silverado, Sierra, Tahoe, Yukon, Suburban, or Escalade from 2007 or newer with a V6 or V8, you've got AFM. You've got those lifters, and they're cycling every single time you drive.

So be the guy who already knew. Not the one I'm scraping metal out of next month.

EDIT: A bunch of folks asked, so here it is. The one I put my faith in is FullForce. This is where to find it:

https://www.tryfullforce.com/products/fullforce™-afm-dfm-disabler

They back it with a 60-day guarantee too. I've handed out more than I can count and not one's ever come back to me. Not one.

See less

[KARNUT]

3 hours ago, diyer2 said:

I've been wrenching on GM trucks for 17 years. And I need to get something off my chest because it's been weighing on me for a long time.

After all that time, all those motors, all those people standing in my bay, I've figured out there are really only two kinds of owners.

The ones who already know about this. And the ones who are about to find out the hard way.

A guy came into my shop a few weeks back in a 2018 Silverado 5.3. Sharp guy, maybe 35. Knew his truck cold. He'd been on the forums, read the threads, done his homework.

He only rolled in so I could double-check a little module he'd already plugged in himself. Wanted a second set of eyes on it. Ten minutes, in and out, drove off happy.

Two days later, a completely different story walked through the same door.

Older fella this time, in a 2016 Sierra. Gorgeous truck, clearly babied, not a scratch on it. Wedding ring. Looked like a guy who took care of his stuff.

He was in because his engine had started knocking on the way to work. And by the time I got the valve cover off, I already knew it was too late.

Lifter collapsed. Cylinder 5. Camshaft chewed up. The whole top end shot.

Same kind of truck. Same motor. Same roads, probably the same dealer. The only thing separating those two men was information.

I've been at this since 2008, and I've worked on everything GM puts out. Silverados. Sierras. Tahoes. Yukons. Suburbans. Escalades. The 5.3 and the 6.2. Doesn't matter which badge is on the tailgate. They all carry the same problem.

So here's the information one of those guys had and the other one didn't.

It's called Active Fuel Management. AFM. GM started building it into their V6s and V8s back in 2007 to squeeze out a little better mileage on the highway. Maybe a mile or two a gallon. All to hit government fuel economy numbers.

The way it works, the motor quietly shuts down half its cylinders when you're just cruising along. And the little lifters that pull that off have a tiny pin inside them that's constantly clicking in and out. Lock, unlock, lock, unlock. Hundreds of times a drive. Thousands of times a week.

Eventually one of those pins wears through. The lifter drops. And it starts grinding the camshaft down like a chisel on butter.

And what nobody tells you is that the shudder you feel around 40 or 50 mph? That's the system cycling. Every single time.

Here's what really gets me. The pre-2007 trucks, the ones without AFM, they're bulletproof. I've got customers still daily driving them with 260,000 miles on the odometer. Not a problem in the world.

GM took a perfectly good motor that would have lasted a lifetime and bolted this system onto it. And it is wrecking engines that should have run forever.

The guys who hang around the forums already know all of this. So do the techs. They handled this years ago. They didn't sit around waiting for the dealership to mail them a warning letter, because that letter is never coming.

It's the guys who figured somebody would've told them who end up on my lift.

And I want to be clear, because this part matters. Maintenance has nothing to do with it. I've torn down motors with barely 30,000 miles on the clock. I pulled apart a Tahoe last summer with 24,000 on it. Practically a brand new truck. Owner had it less than a year.

Spotless oil. Best synthetic money can buy, changed early every time. Made no difference. I've seen guys with full dealer records, every interval stamped. Made no difference.

The oil changes were never the problem. The pin was. And no amount of babying that truck stops that pin from cycling every single time you drive.

That's the part that eats at me. These are good motors. Take the AFM out of the equation and a 5.3 or a 6.2 will run 300,000 miles and never blink.

So a few years ago I started telling every single owner who comes through my doors the exact same thing the smart guys already knew. Get yourself a FullForce disabler.

It plugs right into the port under your dash. Couple of seconds and you're done. It just tells the computer to leave every cylinder running, full time.

No more cycling. No more beating those lifters back and forth every time you turn the key.

It doesn't reprogram anything. Doesn't touch your tune. And unplug it before a dealer visit and there's absolutely zero trace it was ever installed.

I've had customers come back at 40,000, 60,000, 80,000 miles after I put one in. Zero issues. The trucks run smoother. And the lifters aren't getting beaten to death every single drive.

I won't sit here and tell you it's magic. A lifter that's already damaged is a lifter that's already damaged, and this won't un-ring that bell. But it takes away the one thing causing all that wear in the first place. That's the whole game.

You don't need a five-thousand-dollar delete. You don't need an expensive tune. You don't need to tear anything apart. You just need to stop the cycling.

I'm not writing this for any company. I'm writing it because I'm tired of watching the guys who didn't know pay four and five figures for it.

I'm tired of being the guy who has to break the news.

I'm tired of knowing that the guys who did know fixed the whole thing for the price of a tank of gas, and the only difference was that somebody told them first.

If you drive a Silverado, Sierra, Tahoe, Yukon, Suburban, or Escalade from 2007 or newer with a V6 or V8, you've got AFM. You've got those lifters, and they're cycling every single time you drive.

So be the guy who already knew. Not the one I'm scraping metal out of next month.

EDIT: A bunch of folks asked, so here it is. The one I put my faith in is FullForce. This is where to find it:

https://www.tryfullforce.com/products/fullforce™-afm-dfm-disabler

They back it with a 60-day guarantee too. I've handed out more than I can count and not one's ever come back to me. Not one.

See less

When I bought my 14 GMC I turned it off with an handheld programmer. With my 16 Odyssey I left it on solely because I didn’t have much money in the vehicle. There’s a device to turn it off that’s a little more involved. The GMC at 72 MPH the deactivation was on very little the deference was 1/2 mile per gallon. The Odyssey is on over half the time at 72 mph. 

Edited Sunday at 07:37 PM by KARNUT

[TrueBlue]

So, that site says it will work on '23 and up 5.3 (and others). But as far as I think I knew, only Range tech had finally cracked the 23 and up ECM. Do you know if the Full Force disabler actually works on the newest motors and trucks?

 

BTW, I for one appreciate your candidness. I've protected my truck by driving in L9 every time I've used it since I took delivery with 35 miles on the clock, and I'm the only one who drives it, so I'm as assured as I can be that a bad lifter isn't going to grenade my motor. But there are others who have not taken precautions, who could be saved by an honest appraisal of the situation. 

Edited Sunday at 11:29 PM by TrueBlue

[lowrider]

I turned AFM/DFM off on my 22 Silverado with a Range DFM Module:

 

https://www.rangetechnology.com/products/afm-dfm_disabler/parts/RA007

 

Lou

Edited Sunday at 11:36 PM by lowrider

[TrueBlue]

Yes, but the disablers for '22.5 and newer weren't available for a long time after '23. And then only by Range.

This is the first I've heard of another company offering one. Just want to confirm it's a fact.

Edited yesterday at 12:00 AM by TrueBlue

[Atlas]

I never liked the choppiness of AFM (or DFM) in my '15 and '20 Silverados and IMO it's worth disabling just for the driving experience alone.

 

I wonder what the actual failure rate of AFM/DFM is.

[RyanbabZ71]

GMT900 6.2 Trucks didnt have AFM, which was nice.  

 

 

[KARNUT]

2 hours ago, RyanbabZ71 said:

GMT900 6.2 Trucks didnt have AFM, which was nice.  

 

 

I still kick myself for not buying your last truck when you had it for sale. I had two at the time so I passed, damit.

[Grumpy Bear]

On 8/23/2026 at 11:24 AM, diyer2 said:

And what nobody tells you is that the shudder you feel around 40 or 50 mph? That's the system cycling. Every single time.

 

Question @diyer2 on this line if you please. Are you saying the shudder is the system turning on and off at the frequency of the shudder? Guess I'm asking if you are saying you have seen it do this with the bi-direction scan tool in graph mode? If so have you been able to discern the 'trigger'. Something is telling to cycle rapidly. 

 

My truck just started doing this recently. 197K on the clock. My response has been M5 anything under 55 mph. I treat it like a lugging stick shift. Gear down and let it spin a bit. Engauge M5, then tow mode and then M6 lets the trans stay in 5th but the AFM is active. Smooth like Skippy. 

 

My thought was that as a machine ages the friction gets lower and as the system is load based, the lower friction would allow it to turn on at ever lower rpm until it reaches the lugging point. And yes I am ignorant of any minimum rpm requirement for the system. If you know that would be useful information. 

 

As you know I run a Scan-Gauge II which allows me to watch the On/Off of the signal to the VLOM. While in the shudder mode I'm not seeing is cycle at that frequency or at all for that matter outside the triggers @newdude posted a few years back. Now is it possible that the refresh rate isn't fast enough to catch it? Maybe. It is why I asked my first question about graphing and trigging parameter.  

 

As we have observed from members here the failure point is all over the map miles wise as you note yourself in your opening post. That by itself begs a few questions like fellows that comment on these lifters failing even after the system has been disabled. Long after. 

 

https://www.enginelabs.com/news/tech-tips-replacing-ls-active-fuel-management-lifters-with-melling/

 

The Gen5 lifters operate the same as the LS versions. In fact they are the same lifter. 

 

https://www.enginelabs.com/tech-stories/sorting-out-gen-v-lt-lifter-failure-with-a-simple-valvetrain-fix/