hi guys i have a 2021 c8 z51
with only 500 miles
yesterday i was driving and the message came on service transmission and the car had no gear left.
i stoped and restarted the car and i could drive it home but no reverse and the display says no crawling mode available
now when i want to drive it theres no reverse and the R just flashes and it just goes a little back and even when i put it in to neutral so i think its stuck in between gears somehow
any advice where to look first ?
it says code p0796 and 7
p0777 and 6
p0879
it will go forward but also in the wrong gears
i put it into sleep mode and it doesn't make any difference
trans oil is 1 year old and also the filter
thanks

 

Codes come up pressure control issues for a variety of reasons. Get it to the dealer. It's still under the power train warranty. Hopefull a hydraulic system flush and deal with it or perhaps a valve body change. Hopefully it's the former.

 

there is no dealer here because its exported to the Netherlands
i hope its the tcm
or the valve body but i doubt its so easy

 

Get a bi-directional scanner that can do the HSF and give that a try. They aren't expensive and worth the attempt.

 

i do have the scanner and tried everything but no luck

 

what do HSF stands for?maybe i did't try that

 

Wow, no dealer / warranty support
Reads like you have the skills and have researched.
Not knowing the miles since your 1 year ago trans service....
Start with a full battery reset... disconnect for 15 minutes, let sit for 5 minutes, start and idle for 2 minutes, rescan....
1) as mentioned by Mark9, get the scan tool and run a HSF.
2) Then again replace oil & filter with GM products IMO, ie not Valvoline et al.
3) Look for electrical wiring damage from your last service (or any other work).
4) Hoping you have a Service Manual and can check the wiring harness continuity.
5) An oil analysis may (or may not) not be helpful.
6) Artificial Intelligence says, if no change after above....mechatronics/valve body replacement.

All else I can offer is to wish good luck

PS I did once see a Utube video on the transmission valve body replacement along with the internal square large trans. pan filter... might be worth researching.

PSS here’s the A.I. entire sequence in one clean list:Check fluid level & condition

1. Battery reset / TCM power cycle
   
2. Run HSF hydraulic flush routine
   
3. Inspect wiring & connectors
   
4. Check live pressure sensor data
   
5. Command solenoid tests
   
6. Run clutch learn / fast‑fill routines
   
7. Replace mechatronics/valve body if tests fail
   
8. Replace TCM only if all else passes
   
   Again, good luck
   

 

yes i did see the video to i am thinking about that
i think its something electric i did all the flush procedures but it didn't help it
when i reset / disconnect the battery over night its saying service trans before i even start it
i checked alle the connections and they are fine i also have comunication with the tcm

 

I had EXACTLY the symptoms you describe on my '21 and a new valve body corrected the problem.

 

I knew GM sold Opel years ago but if it's still exporting European spec Corvettes to Europe it's crazy that there is no support for service and warranty issues. I sure hope you can figure out what is going on with your car.

 

Hydraulic System Flush, not to be confused with other use of the term flush. It is a scan tool initiated procedure in the TCM software that actuates the solenoids (in the valve bodies) in a specific manner to flush debris from the system. The debris, if any, that is flushed from the system is moved to the external canister filter. It does not involve any replacement of transmission fluid. When used in a diagnostic procedure in an attempt to remedy a transmission problem, it is often followed by replacement of the filter. When that is done, a small amount of fluid is lost, and should be replaced. After that Transmission Fluid Level Check should be performed. This process has often resolved transmission issues, but not always.

 

2021 and 500 miles ?the transmission died of boredom and a list of other things that are going to give you more issues like fluids for starters

 

thanks i will look in to that

 

Good Luck with the fix.

 

Probably valvebody. That being said your codes are a bit different than mine so a comm issue as stated above isn’t impossible since recent service. So don’t assume this is it. You should also have a p0700 code in there somewhere. (This is normally the code that tells it to trip the CEL light)Try the flush procedure a few times as stated above but once they fail like that usually it won’t work. That only worked for me if still moving on its own power and has gears again after sitting. Dumping fluid and filter change may work if you can get it going again w battery reset. The valve body install isn’t awful to do yourself since you are in another country.

below is what mine did and my codes



this is what I did to fix it myself.




i am still running valvoline DCT fluid if you have no warranty there may wanna save a few bucks as I recommend replacing twice if you end up changing valve body so you truly get all of it out as some residual quarts will stay in the clutches and differential.

also go on eBay and download the service manual for cheap it will be a huge help when doing the valve body as my video skips some parts due to making the video too long. They have service manual copies for cheap in pdf you can get via SD card.

let us know what you all find so we can all learn.


also while you have the lower panel off do yourself a favor and save time doing the dct panel door. It’s gonna save you a lot of time in the future . I personally know people on their third valve body.

Do the mod while the panel is off and not how I did it. Much easier and safer. This will show you part numbers tho on what to order.

 

Was the transmission fluid changed at the 3 year mark?

 

He said “trans oil is 1 year old and also the filter” and has a 2021…

 

There is no Chevy support at all in the Netherlands?