And like others said - the callout for performing a maintenance procedure in the Owner's Manual does not cite all the steps in a maintenance procedure. I suppose you can't be convinced further, and I suppose it does not matter. But there are few examples of other non-trivial procedures that are not called out in the manual but are part of the procedure. If you skip one, can a problem develop and will it be a warranty issue? Take a simple one first - it calls for replacing the filter cover bolts with new bolts. Is it a problem if you dont? Next - the procedure calls out another procedure "Transmission Fluid Level and Condition Check". Is it an "important maintenance item"? Its a 19 step procedure that involve running the engine for 3-5 minutes, cycling the transmission between D and R, then putting on the lift, and checking the fluid level. Probably takes about the same length of time as the hydraulic system flush. If you skip it and have low fluid is it a warranty issue? Would you want to skip it? But, we're not done yet. As one of the last steps, the DCT External Canister Filter Replacement Procedure includes a Hydraulic System Leak Test which - guess what - requires a scan tool to execute. It takes a minute to execute according to the procedure. I do not know if all dealers do that, but I would expect them to check for leaks one way or another -as done when an engine oil filter is changed. One could argue that since the Owner Manual does not say "Change the DCT external cansister filter: perform the hydraulic system flush , remove and replace the cansister filter, replace the fluid filter cover bolts and seal, top off the transmission fluid, and check for leaks" then those bolded steps are not important and could be skipped. Asking if the individual steps in a procedure are "mandatory" is problematic. The question is, if I skip those step, can it result in a transmission issue, and if so, will it be covered by the warranty (if the steps were skipped)? The answers are yes, and maybe/maybe not.

 

I truly don't understand how you continue to miss the point on this. In your owners manual it doesn't give you step by step instructions on how to change the engine oil. Nor does it for the DCT filter change. There is a procedure on how to change the DCT filter, and that procedure clearly states to conduct the flush first.

Lastly, with the issues we have seen with the DCT why on earth would you bypass this step? I have had to have my DCT valve body replaced twice for solenoid/sensor related plugging issues. Others have as well. The flush is an essential step to attempt to keep debris out of the valve body and keep the DCT operating smoothly.

I realize you like to do your own maintenance. I do as well and is why I have a quick jack to do so. But I won't be changing my own DCT filter as I can't do the flush which the procedure clearly calls for - and there is no way in hell I want to jeopardize the warranty on the DCT with the issues we have seen with it.

 

Or just buy an mdi2 clone and document that you did the flush yourself if there's ever any warranty issues

 

I think he already agreed its an important maintenance item - in post 18. And his dealer so indicated it. Of interest in post 18, his dealer mentioned that they had two in the shop with transmission issues that did not change the filter in accordance with the schedule and are now having transmission issues that will probably not be covered. That's actually a pretty important report.......I don't think we have had many if any reports of actual warranty denial resulting from a failure to replace the filter on schedule.

 

You're looking in the wrong place. The owner's manual doesn't tell you HOW to do the required maintenance items, only when they should be done. The owner's manual doesn't tell you that when you change the oil filter you need to lubricate the gasket on the new one. But that's an important part of the oil change maintenance that is (I assume) described in the service manual procedure. The OM doesn't tell you that changing the DCT filter requires you to install new gaskets, but if you don't want it to leak that's an important part of this maintenance item that is specified in the service manual procedure. It doesn't even tell you that you must bleed all the air out of the cooling system after you drain and refill the antifreeze at 150,000 miles. The service manual specifies that as part of the maintenance procedure.

The owner's manual tells you what the routine maintenance items are.

The service manual describes how: the procedures to be followed for those maintenance items.

The procedure defined in the service manual for the DCT filter change maintenance specifies the flush as part of this maintenance procedure.

 

Seems like the word "flush" in the procedure creates confusion for some. Its reminiscent of the old procedure for draining fluid and flushing out the transmission housing - or the more recent BG transmission flush that requires external tubes to be attached and "reverse flushes" the lines. Some even equate it to the 3 year transmission fluid drain and fill - mistakenly calling it a flush or flush and fill. Its not any of those things. In post 18, the OPs dealer even seems to have said it wrong : "Bob Stall Chevrolet, La Mesa CA has just called me back and stated that yes the DCT Hydraulic System Flush is very necessary and should definitely be done at the three year mark (they do it all the time)" It is a computer manipulation of the solenoid actuated valves while the engine is idling with a goal of freeing any debris that may be trapped in the valves or lines and moving it to the filter before it is changed. In the Service Manual there are individual "Transmission Service Cleaning Procedures". Each one is executed from a computer or scan tool and each one address one or more of the solenoid actuated valves in the transmission. I believe that that Hydraulic System Flush" executes one or more of the procedures in a specific sequence. Perhaps the Hydraulic System Flush step would be less confusing if it said "Perform the Hydraulic Control System Sequential Cleaning Procedure"......or anything but flush.

 

Sorry for confusing some of you (American English is not my first language) - My BAD. Allow me to try some more...
1) I don't want to know HOW to do anything and I'm therefore not asking for the procedure!!
2) I do want to know where it states / documents that I need to have this "Hydraulic System Flush" done.
3) Lots of kind folks have taken their time and made the effort to post docs etc. showing the procedure - Many THX!!
Moving on. The 2020 Owners Manual (OM) is the only document regarding maintenance that was given to me as an owner / operator. On pg. 290, Footnote # 4, that OM states that I need to change / replace the DCT fluid every three years and also it says to change / replace the DCT filter. OK Fine By Me I can do that - no problem. And to be fair, at the end of Footnote #4 it adds these two lines: "This service can be complex. See your dealer". Well if it weren't for all the noise (music?) on this forum about a "Hydraulic System Flush" I would not have bothered to, ".... see your dealer". So a BIG thank you to the knowledgeable forum members who share their wisdom.
I don't currently own a 2020 C8 service manual but I'm considering buying one - eventually ;>)

 

I wonder what is different in the "manipulation of the solenoid actuated valves" verses what they do, or don't do, during normal driving sequences? I'm guessing that all the valves have a reason to be there and so I would think that during a normal driving sequence that they would all be called on to operate at some point. Does anyone have insight into what actually happens during the procedure? Valves "stroked" longer; reverse flow at some valves; higher fluid pressure/flow rate?

As-to having the procedure completed at the dealer and then driving home to change the filter oneself, my only concern with that - and it's a relatively small one - is that if for some reason the procedure did dump a fair amount of debris into the filter to where the filter by-pass valve opened, then a significant amount of the debris could/would be washed off the dirty side of the filter and into the DCT; that would defeat all the benefits of the procedure and the filter at that point.

 

"Owners manuals do not list steps in procedures."
@bhvrdr Not to put too fine a point on it... but I refer you to pg. 220 of the 2020 Owners Manual for a detailed procedure regarding - YES - changing the engine oil & filter (of all things).

 

Hope you have a good sense of humor

 

You are correct as I should have said "owners manuals do not list steps for every procedure."

​​​​​​There are many maintenance procedures not outlined in the manual of how to complete.

Changing the DCT filter is just one of them

 

Sorry, but you're still refusing to get it.

The point is that the owners manual only tells you when a service is to be done.

The SERVICE MANUAL tells you (or the dealer) what that service includes.

The DCT filter change service INCLUDES the flush procedure.

At this point, I think you're deliberately refusing to acknowledge the facts. Every service listed in the owners manual includes multiple steps. Those steps are not listed in the owners manual, but in the service manual. The first step in the DCT filter change is to do the flush. Nothing difficult or complicated about that at all. It doesn't say "only during a repair," or "only when you change the fluid." Nor does it have any other qualifiers. The First Step in the DCT filter change is to do the flush. Period.

 

The owners manual lists the procedures for maintenance items that (in GM's view) can be performed by the owner. For the DCT filter change the owners manual has the statement "This service can be complex. See your dealer." Probably for the very reason that people might not know how to interpret the service procedures.

 

I have no knowledge of what it might be. But I can speculate that the valves are operated in a different way - for example the could be cycled at a high rate. There is also some pressure regulation in there. They could be operated at a higher pressure. Things like that. Also, there is no indication that any of the flow ever "reverses" That being the case, I think (reasonable assumption) that the fluid returns to the fluid pan before going back to the filter. That is, I believe (hope) that the valves are downstream from the filter and receiving filtered fluid. So that fluid likely returns to the pan, then gets drawn back into the filter. All speculation. There are magnets in the pan to trap any ferrous metal if there is any.

 

@Andybump That's a great looking graphic!! A lot of work and I do understand the circular thinking.... BUT bare w/me here - THX. You see I'm expecting that my Owners Manual will actually: "Show Me When Important Maintenance Items are REQUIRED to be SCHEDULED & Done".
Now about the circular thinking... The docs from forum members are from a Service Manual, so understandably those docs describe HOW to perform the Hydraulic System Flush process (The Procedure). The Owners Manual fails to mention when to have this maintenance scheduled (Where Is It Documented?). The emphasis is on the schedule not on the process.
The DCT is very expensive and its maintenance is very important - so I'm surprised that a Hydraulic System Flush event schedule is not mentioned as a necessary maintenance item in the only manual that buyers receive with their purchase of a C8 - The Owners Manual.

 

The hydraulic system flush is not a maintenance item. It's a step in replacing the DCT filter which is a maintenance item.

The manual says when to replace the DCT filter. It says it in a nice table and again in written language.


If you plan on doing your own maintenance it behoves you to know how to do them... which means becoming familiar with the service manual not just an owners manual.

 

@Red Mist Rulz Actually my point is that the 2020 Owners Manual does NOT tell me when a Hydraulic System Flush needs to be scheduled - it says change the DCT filter at three year intervals. That's why I was looking for any docs that mention scheduling a Hydraulic System Flush. "Nothing difficult or complicated about that at all."
Lastly, the DCT filter change does NOT require a flush procedure every time (thus the confusion).

 

Clearly you are trolling now.

You don't SCHEDULE a hydraulic system flush. It is a step that is required in changing the external DCT filter.

You already have the schedule for the DCT filter change.

I have no idea where you found an alternate DCT filter change procedure that doesn't require the hydraulic system flush but I have yet to see that.

 

Thank you for all your appreciate sage advice regarding what a DCT filter change in the Owners Manual means!! I've scheduled the official three year DCT fluid replacement & filter change w/my dealer so all will be properly done on time. In the past I simply replaced the DCT filter myself (per ) and of course I did not know that a hydraulic system flush was a required step (nor did I have the software)... I'll have a chat w/the service manager when I bring my car in.

 

Correct me if I am wrong… I think the flush procedure was added after the trans started to have failures/ issues.
The speculation was that the clutch’s where creating debris that GM wanted removed from the areas in the valve body. ???
And now we have this extra step before replacing the filter.