Finally had enough of being without the car and called GM customer service to ask for a rental. They told me that I have to rent the car and then once the repair is complete, I can submit for reimbursement which may or may not be approved. A customer being without their $90K car due to problematic transmission design, incompetent dealer techs and inability to source parts is not grounds for GM just proactively approving the rental. Tell me you're not going to approve reimbursement without telling me you're not going to approve it. What a joke.

 

Interesting - the C7 8l90, though totally unrelated, had the exact same symptom for a similar issue -Valve body solenoid. Hope they get it fixed.

 

I'm just worried that with all the stalling and slipping and god knows what else going on that the clutches are damaged or the gearbox is now compromised. If it is not shifting and behaving absolutely flawlessly when I get it back, I'm immediately dumping the car. Don't think I'll get another C8 after this.

 

If you're worried about it, why not get the +7 years of GM extended warranty for like $2k through Macmulkin? That iterally gives you 10 years of worry-free driving of this car for so cheap, which is unheard of in the supercar world.

It would cost you 3x that in sales tax to the government to switch to another car...

 

Sales tax in my state on cars is 3.5% of the sale price less the trade. It'd be about a grand in tax give or take to get into another $90K car. I don't need an extended warranty because I'd never keep a car that long anyhow. If having warranty was the cure-all, I would be having a great time now (in warranty). The warranty is not the problem, fixing the car and GM's poor dealership service and customer service practices are the problem.

 

If you sell the car before the GM extended warranty ends, you get a pro-rated refund. Or you can transfer it to the new owner (you'd be able to sell the car for more, likely for at least as much as the GM extended warranty costs).

 

It's acting like it's low on fluid. I know I lost creep when mine had fluid changed and it was low. Got fluid in it and everything went back to normal.

 

How low was it?

 

I don't know, it was after I pulled the airbox and added the two extra quarts that everything was normal again.

 

Valve body is at the dealer but it'll be another week before they can get to it. First whiff of this thing acting up when I get it back and I'm going to get rid of it. 6 weeks without the car is absolutely unacceptable.

 

I see they had GM involved. Was there still no DTC? There are two valve bodies - and when there is a DTC they follow procedures to determine which valve body to replace. I wonder how they made that determination without that? And, as I noted earlier - the procedures I see for many/most transmission issue include attempts to resolve it (under warranty I thought) by doing a Hydraulic System Flush, replacing the external canister filter, replacing the fluid, and even replacing the internal canister filter, all before replacing the valve body. Maybe they did some of this? Given that how the procedure written by GM work, I would have expected GM to advise them to try all of that before jumping to valve body replacement. Now, there are some issues and codes that may jump more quickly to a valve body replacement - but in absence of a code ??? I guess we'll never know. But its good that they are trying something.

 

It may have finally given codes. Not sure to be honest but I'll ask the tech. He said the problem is actually masked when starting, letting it warm a bit and then reversing first (pretty much the way I drive on every cold start). He said from cold trying to go direct to drive had the car bucking like crazy. He told the GM field rep that the car is absolutely undriveable.

 

When I first crank the car, I let it warm for a couple of minutes. Once I back up and put it into drive, vehicle jumps and bucks like crazy. It seems to want to jump from the V8 mode to the V4 mode even in 5 - 10 mph. I see the display showing it jumping from V4 to V8 repeatedly. It makes no sense. After the car warms up, it does not do it. I took it to the dealer, they could not replicate it. Of course, I don't think they tried very hard. It was still warm. I asked if they could reset the V4 mode only to kick in at over 40 miles an hour but he said he did not think so. It has been very frustrating. I have a 2023 Z51, HTC, 2LT.

 

There are a bunch of conditions that must be met for V4 to be enabled. Here a few from the 2020 Service Manual I have (they could have changed):
coolant temp above 100 def F
speed greater than 15.5 mph
rpm between 700-2800

And, you need to be in a steady cruise (not for long) with very light throttle.

And as you already know, even if/when it kicks in, the car should not buck - it should be a relatively smooth transition - many cannot detect it.

 

For the record, my car finally did store codes 3 weeks into the process. The codes are what prompted GM to advise valve body replacement. Car is still sitting in the dealer's dirty back lot and has not been touched.

 

My problem is identical. Only when cold start. Once warm. No problems. Tried in Track Mode and Sport Mode, cold start, to eliminate the V8 to V4 changeover and still had the same issue ALTHOUGH not as bad.

Dealer scheduled appt. They are 3 hours away! I have zero confidence they can solve issue without more Chev HQ involvement and providing info from others around the country.

It is strange that is does not have isaues after it warms up.

 

Dealer suspects the problem is related to the valve body. Lots of issues with 2023 Z51 and most have involved replacing the valve body or the entire transmission. Many owners with similar issues. The new replaced VB seemed to have fix the issues. I guess we wil see what happens with yours and mine.

 

This Bulletin involves the Camshaft Actuator Magnet. If it is off by more than four degrees, the engine will shutter and jerk in low gears and it makes one think it's a transmission problem when it is not. I took my car to the dealer this morning and after searching numerous bulletins this one was discovered. It came out originally in April 2022 and only covered Corvettes, and many other GM vehicles from 2014 to 2022. An update just came out 5 days ago and now includes all of those vehicles through 2025!

​​​​​​There's a diagnostic test that can be done by the technician and it will show a graph. If the degree offset is more than four degrees, the graph will be all over the place. Mine was out of balance. The fix is to replace the camshaft magnet. That involves multiple hours of work and, yes, you do have to drop the engine!

The technician is confident that this will solve the problem. Having driven it for 3 hours to get to the dealer, I noticed that it was shuttering slightly at high speeds as well. Even when warm, the car will continue to have a slight shutter and shake but not as bad as when it starts cold. Beyond a code engine start, when the car jerks and Shakes and low gears like the bottom is going to fall out from under it, the Telltale sign is when you're running a steady 70 miles an hour and your RPM needle is bouncing repeatedly.

If you search for the Bulletin by its number, only the April 2022 version is available at this point on the web. I have not found the updated version the dealer was able to pull from chevrolet.

See the below 2 links:

https://www.corvetteforum.com/forums...209d1654289877

https://www.midenginecorvetteforum.c...ne-shudder-fix