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

[Tod Chretien]

I don't think it's the AFM killing the transmission as much as the 
problems that the transmission possesses. The pressure regulator valve 
wearing so bad is a good example. I personally think the AFM can cause 
misdiagnosis of a shudder but I don't believe the AFM actually causes 
the transmission to shudder. That's just my opinion. Turning off the AFM 
does wonders for the driveability of these trucks and I hate how doing 
that is illegal in the State of California.

I'm sure the dealerships don't recommend a complete engine when the 
vehicle is still under warranty! But hey, if the customer is paying for 
it, take him/her to the cleaners! It really ticks me off how *most* 
dealerships are so incompetent and dishonest these days. We get vehicles 
in here all the time that the dealer said it needs a transmission when 
all it really just needs is a minor repair. Their story always states 
they found metal flakes on the dipstick. Give me a break! Your not going 
to find metal flakes until you remove the pan.

/[[ 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. ]]/

If the AFM is causing the transmission to fail, then how in the world 
does replacing the engine (or the AFM components) save the transmission 
when it still has the AFM programmed in?

Forgive me if my post sounds condemning. I'm a little disgruntled from 
recently buying one of these trucks (used) and having an AFM lifter 
collapse three weeks after ownership.

-- 
Best Regards,
Tod Chretien
TRNW Inc.
https://www.trnw.net

On 6/17/2025 5:52 PM, Tony's Autoworks via trnw2 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
> This message was sent from the TRNW Technical Discussion Forum (trnw2). You were sent this message because you have subscribed to our mailing list. If you don't want to receive these emails from TRNW in the future, please unsubscribe here:
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> TRNW Inc., 2825 Walnut Terrace, Modesto, CA 95355
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