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

Wed Jun 18 10:46:31 PDT 2025

Thank you all for your comments. I talked to another transmission shop
this morning and this situation has just the new kid in the block when
it comes to engine issues that can't be diagnosed before the
transmission rebuild. In the end, we can only fix what we see to be
broken. From there, just make the best of the situation.  I have the
HP Tuner and have used it mainly to copy and paste techem software and
for live data diagnosis. I can use it to disable the AFM and am
looking at what to change for the TCC lock up strategy. As we are
starting to see the 4L60's fade away and the 6L80's clocking over
100K, I guess we do what we have always done. Roll with the punches.

Tony

On Wed, Jun 18, 2025 at 10:25 AM Steve Everett via trnw2 <trnw2 at trnw.net> wrote:
>
>
>   As Dan said , if the customer brings the vehicle in when they first notice the tcc shudder,  those clutches will be like new, and the pump won't be damaged enough to worry about,  usually not damaged at all ,   there might be a teaspoon of material in the pan,  the PR valve will be worn, and the tcc reg valve bore will be worn,  address those and delay lockup until 5th gear , I usually set them around 45mph,   the exception being if its a truck that tows around town I'll have it lockup in 4th gear and at 40mph,   so that it will lockup at around town speeds and not overheat while towing
>
>     Steve
>
> On Wed, Jun 18, 2025 at 12:46 PM Dan Hogan via trnw2 <trnw2 at trnw.net> wrote:
>>
>> 456 clutch failures are not related to AFM in my opinion.  I agree with Steve as most 456 failures are the result of excessive metal debris related to converter issues resulting in restricted pressure and sticking valves / filters.  Customers who bring their vehicles on the front end of converter failures tend to have intact 456 clutches.  The ones who keep on getting it until the vehicle won't move or slipping badly on highway drives tend to arrive with a roasted 456 clutch.  Usually can hear the pump whining at this point as well.
>>
>> How are you dealing with the converter clutch failure debris in the cooler system?  We still have local shops who don't flush or do anything besides a can of flush and install a unit or rebuild and wonder why they have repeat failures.  I don't do carry-out work anymore as I don't want to fight these folks. The amount of debris from these failures is significant.  Even hot flushes sometimes don't get all the debris out of the system.
>>
>> I'd look over your methods to manage contamination as it's a big deal and I suspect the main cause of rework.
>>
>> Now diagnosing AFM malfunctions vs TCC shudder can be difficult and most dealers don't have the personnel to do fine level diag work from what I see and hear now.  It's just swap until fixed and customer gets to pay.  I don't recommend any young folks get involved with dealers at all anymore.
>>
>>
>>
>> ---
>>
>>
>> Dan Hogan
>>
>> Buster's Transmission Service
>>
>> https://busterstransmission.com
>>
>> 704.847.5321
>>
>> ________________________________
>> From: trnw2-bounces at trnw.net <trnw2-bounces at trnw.net> on behalf of Tony's Autoworks via trnw2 <trnw2 at trnw.net>
>> Sent: Tuesday, June 17, 2025 8:52 PM
>> To: Technical Discussion Forum <trnw2 at trnw.net>
>> Subject: TRNW-2: Chevy Active Fuel Management Killing 6L80's?
>>
>> 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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