I truly appreciate all the knowledge, expertise and guidance the folks on this forum provide. Although I am a corvette enthusiast, I am far from being a mechanic! I would like some opinions on my recent issue. I own a 2023 C8 with 1,100 miles. Unfortunately, my long work hours prevented me from enjoying the car. Since I retired this year, I have had the opportunity to drive the car more often. A few weeks ago, the transmission warning light came on. I stopped driving the car. Yesterday I took it to the dealer and the light had gone out and did not come back on. (Also disappeared from my phone app). However, the dealer stated that they discovered a p700 code (valve body), and a p2855 code (clutch one pressure charge performance). They kept the car and are going to drive the car to see if they can recreate the warning light to try to retrieve more codes to help with the diagnosis. Are these codes detecting serious issue with the transmission? Should I be concerned? Any opinions/thoughts? I was really surprised considering that I don't "beat" the car and it only has 1,100 miles. Thanks in advance for your help!

 

Hard to know what the eventuality will be but I'm guessing that it's something that a hydraulic system flush and perhaps a relearn can't address. I've had transmission codes come up, cleared them and nothing since. MY23 with 11000 miles and 30 track days. You should be covered by the 5yr/60 mile powertrain warranty so worry not.

 

Thank you. It is just concerning! I appreciate your reply.

 

It could need the valve body replaced, but the first thing I would do is a Hydraulic system flush, fluid replacement, filter replacement, in this order.

 

There have been many issues with the C8 trans, and many have commented on here about experiencing them. The step process is the Flush and Relearn. If that fails, then the Trans Valve Body gets replaced, and if that fails, you guessed it, full trans replaced. The good news is that the Trans Valve Body replacement has solved almost all issues that I have seen and heard - including from my servicing dealer - as the new TVB is better for sure.

Either way. Good Luck with it. My 2023 HTC Z51 started shuddering and running strangely last fall. Thought it was cold weather related but as the Spring came and it warmed up, it continued. I took it to the dealer and found the Camshaft Actuator Magnet was bad and was sticking. It controls the timing. Never threw a code until a few weeks after the service visits, and while waiting for parts to come in. The really bad news is that its a $30 part but the entire bumper, exhaust, AC and lines, have to be removed and the ENGINE has to dropped just to install something that is about 4" in diameter! Over $8000 in warranty costs. See Technical Service Bulletin 2022 - NA -080. That bulleting covers cars and trucks with the 6.2 L engine from 2014 - 2025! I almost wish it had been the trans valve body considering the amount of work that has to be done to replace one little stupid part. GM is paying a ton of money out for warranty work on these 6.2L engines. They have a full recall out for a internal engine piston rod connector part that is failing, so all 2021 - 2025 SUVs and Trucks have to be recalled and the ENGINE REPLACED!!!!! Over 800,000 worldwide!!!

I just took my car in this week for the work to be completed. Oddly, the Check Engine light went off last week but the code remained. CAM timing issue!

 

I appreciate the comments and advice. Thank you! Hopefully the dealer is aware of these steps. There was a 2023 at the dealer when I was there and I was told it needed a complete transmission replacement! TEvans your issues are just crazy! I would have been upset. I hope I don't experience many more issues! As I mentioned, it is very disappointing considering that I have only driven the car 1,100 miles.

 

Agree with above posters, flush procedure, change fluid and change at least the serviceable filter. I ended up having to do a full valve body replacement. It's not really that bad to be honest and they should have no trouble fixing it . Sounds like you have some early signs of possible contaminants which could end up being nothing or as stated above be as bad as a whole DCT replacement (less likely). I'm still trying to find a company to take apart my failed VB and figure out source of failure +/- rebuild it. If no luck I may find a way to test myself and try to find failure source. Good luck and please report back what ends up being the solution so we all can learn.

 

Thank you! I will report back once I have info. As I had stated, the warning light is no longer illuminating, but they are getting codes. They preferred keeping the car a few days to drive and diagnose. Again, thanks!

 

It's a longshot the dealer tech will have any clue.

 

The P0700 code does not convey any information other than that the TCM has requested that the Malfunction Indicator Lamp (MIL) (aka the CEL) to illuminate. The other code is the important one. And P2855 says "P2855 .....B12BA Transmission Fluid Pressure Sensor 1 = Greater than a predefined threshold". A pressure sensor has detected an out of range value.

According to the manual I have, if that code is active, clutch 1 will be disabled. So, if your car is now driving normally, I think that code is not active.

Most of the transmission related diagnostic procedures focus on active DTCs. The procedures, as describe above in this thread, will step though a series or possible remedies, clearing the code after each attempt, and if the code does not come back its done. It say a low fluid level can cause it so that is the first check (but since your code appears to be the overpressure indication, I'm not sure how low fluid could cause that). Then goes to the Hydraulic System Flush (I have an older 2020 manual that refers to "cleaning procedures" but I think that has been replaced with the HSF procedure.). Its followed by replacement of the external canister filter, then fluid replacement, then replacement of the internal filter which involves removing the transmission pan. Then transmissoin replacement. Mine does not indicate a valve body replacement as step - but the manuals are updated regularly so that could included now. And, also, there are now more field repairs allowed.

Thing is, if you don't have an active code, and if the car is now behaving properly, there is not much the dealer can do.

 

Yep in 2020 and 2021 there were a number of posts where members early low mileage DCT CELs (there are over 100 #s as I recall from a GM Tech who serviced about 50) and when they brought the car to the dealer, Tech called GM Service and read the code # to them. Many were told to just do a Flush, no new fluid or filter just a Flush. That is done by the GM service computer connected to your cars OBD port. Thanks about ~10 minutes. The engine runs at 2000 rpm while “things” in the DCT cycle. The GM procedure says it moves possible debris clogging a Valve, Solenoid etc and moves it to the DCT filter. Most reported CEL was gone and did not come back.

Possible since your CEL is gone it cleared itself. Dealer will look for a memorized code if it was saved and probably call GM service who will advise if a Flush should be done. Cheap to do as no fluid or new filter added. It’s performed with the car on the ground no lift needed. I watched as Tech did my 2020 C8 year 1 with ~3000 miles as pert of my free GM replacement of the DCT filter offer. He did it again year 3 as part of the required DCT filter replacement between 7000 and 8000 miles.


Expect it wil be done on my two year E-Ray service there I will have from 7500 to just under 8000 miles and the new DCT filter with flush will be done on GMs dime.

 

Wow! Great detailed information! Thanks for taking the time to share!

 

Great, detailed info! Thanks for taking the time to share everyone! I appreciate it! As I stated, I am far from being a mechanic and respect all the knowledge on this forum!

 

[QUOTE=TEvans;1609175555] GM is paying a ton of money out for warranty work on these 6.2L engines. They have a full recall out for a internal engine piston rod connector part that is failing, so all 2021 - 2025 SUVs and Trucks have to be recalled and the ENGINE REPLACED!!!!! Over 800,000 worldwide!!!
/[QUOTE]

The service bulletin you referenced is for LM2 engines, not the LT2. My neighbor has a 2024 GMC pickup with the L87 6.2 engine and it was recalled to check for a manufacturing defect in the connecting rod and/or crankshaft. Upon inspection, his only need to have the engine oil changed to a different viscosity. Some inspections revealed a full engine replacement was in order. That was a different service bulletin.

Neither were related to the Corvette C8 LT2.

 

So.....here is my update. I hope I am sharing this accurately. My apologies if some statements are not totally correct. The car was at the dealership from Thursday until yesterday. As I had stated in my initial post, my warning light was no longer on when I took the car for an annual inspection, oil change and to check to transmission warning light. They tried, but were unable to recreate the warning light. In addition, they stated that when they they performed the PA emissions check, the diagnostic unit was still kicking out a code preventing them from inspecting the car. (The dealer stated that they did a reset of the codes). They asked to keep the car, drive it for a bit to try to reset the codes. They drove the car for over 100 miles and the codes still did not reset. They told me to pick up the car and drive it for another hundred miles to see if the codes reset or if the warning light returns. The car seems fine. No issues with performance. They stated that they cannot perform any work on the transmission without a warning light. GM may not honor the warranty work if there was no proof that an issue was occurring. Stay tuned.......

 

That is "mostly" true without a code. However, if the transmission were showing performance symptoms without a code, they can contact GM for advice, and do certain things they indicate. But in your case, "the car seems fine. No issues with performance." So, that leaves them with nothing to go on. And honestly, in that situation with no codes and no performance issues, I would probably be satisfied to leave it alone for now.