TRNW-2: Chevy Active Fuel Management Killing 6L80's?

[Justin Merritt]

Seems what you are feeling in the dreaded gm AFM drone. I had a 15 model 1500 that had that drone/ vibration at 40k when I bought it. The easiest way I have found to address the vibration in the 6Ls tuning with hp tuner. Turn the dod/ afm off, and tune the Tcc to your likes. Most tune Tcc apply to 5th and 6th gear, and raise the mph for engagement. If you havent  bought and used hp tuner, it is a very valuable tool that will pay itself back really quickly rebuilding 6Ls.  

Justin 
Sent from my iPhone

> On Jun 17, 2025, at 7:52 PM, Tony's Autoworks via trnw2 <trnw2 at trnw.net> wrote:
> 
> Hello group,
> 
> Wanted to get an opinion of what I have seen over the last 3 months. I
> have rebuilt six 6L80/6L90 and have had a few other vehicles come in
> the door with similar problems that I will explain in a moment. Of the
> 6 I rebuilt, all had 4-5-6 clutch stacks completely burnt and 3 of the
> 6 had pumps that were not reusable. Of the 6, 2 of them were towed in
> with no movement. Just finished the 2nd of the two yesterday and
> completed a test drive for the new techem to adapt. But noticed both
> towed in units having some issues but could not determine the cause
> until now. After a certain amount of time test driving I'm noticing
> rpm fluctuations and an intermittent shudder noise on the most recent
> unit. Checking scan tool data the TCC is applying and no TCC RPM slip
> is occurring when the shudder happens. I noticed the same issues on
> the last unit but NO shudder until today the customer told me he
> experienced it and I just test drove to confirm.
> 
> I also have a customer with a 2015 Suburban that had a transmission
> installed a few weeks prior from a different city and started
> experiencing the shudder issue. He thought maybe he had a defective
> torque converter. I noticed the shudder in the Suburban sounded
> different from the shudder in the silverados so I thought maybe the
> converter was defective. The suburban customer took the vehicle to the
> dealership and they diagnosed the Active Fuel Management causing the
> shudder when the system is activated and recommended a new engine or
> complete replacement of all AFM components.
> 
> I took my recent rebuild on another test drive and with the traction
> control off (a friend from the chevy dealer advised this test) and now
> there are no RPM fluctuations and no shudder. Same with the other unit
> with similar issues.
> 
> So now I have 2 units that have been rebuilt that looks like the
> Cylinder displacement may have been the cause of failure? My friend at
> the Chevy dealer says they are seeing a lot of these units come in and
> if they catch them in time they can save the transmissions. And most
> are replacing the engine rather than components.
> 
> My question is this: Unless there are engine codes to know that the
> Cylinder displacement is an issue, how do we sell the build?
> Especially if the vehicle can not be test driven. I have 2 customers
> that have spent money on rebuilt units but now are looking at twice as
> much to fix the engine issues.
> 
> I'm sure this topic has come up before and I guess I missed the memo.
> Just curious of your opinion and what have you done to diagnose this
> issue before selling a build.
> 
> Thanks for reading,
> Tony
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