[BRKGBAD]

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[Mark114]

You can see if the engine is in V4 or V8 mode with the Information page on the DIC. That may help you correlate AFM (V4 mode) with specific behavior. You can effectively disable V4 mode by putting the transmission in Manual mode, downshift, and upshift. As long as you keep the transmission in Manual mode the engine will stay in V8 mode.

The ECU/TCU is programmed to automatically downshift the transmission to help braking. The behavior is different between modes (Snow/Ice, Tour, Sport, Track). Try a different mode to see if the downshift changes.

In the end I believe the service tech will have to document a problem before GM will reimburse the dealership for specific service procedures and replacement. Per the TSBs there are specific tests that have to be performed and documented with service equipment monitoring the engine and transmission. A "seat of the pants" diagnosis probably won't be good enough for the dealer to be reimbursed. Most dealerships won't pay for parts replacement out of their own pocket. I suggest you discuss the game plan with the service tech prior to the drive.

Good luck! Mine goes back to the dealer tomorrow to see if the latest fluid flush will resolve shudder on mine.

[BRKGBAD]

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[Eric10905]

Originally Posted by BRKGBAD

Unfortunately when they did the 2nd flush, the downshifting problem went away. Out of boredom I google'd around about Valve Body issues and apparently one big issue is downshifting. Maybe I have an issue there...who knows.

I'm hoping to stop for a test drive sometime this week. Love the car, looks great and is very fast, but I just want it to drive normal for once. I've had it over a year now and its only driven correctly for a few weeks.

Hey Brkgbad,

I feel your pain. Had mine for about 6 months now, and been back to dealer too many times... h

I took mine in last week for the second time on shudder. Trying to not be too verbose here... first time they said, oh, there was a transmission update, and after we installed it, there was no shuddering. BS... i had it shuddering slightly before i got it home that day. So, weeks later (just last week), I finally took it back in and told them about the shudder again. And that also at times it was shifting really oddly and/or hard. But it had not done it enough times for me to be able to properly characterize it. On Saturday, the tech left me message saying it skipped second gear and went to third on him. And somehow he was going to have to replace the entire valve body. And that was an order item, so it might not be in and installed within this week of the 4th. Wasn't able to reach him after that.
Not sure if that helps any at all... but for what it's worth. if you like, i'll post an update once they call again, or when I can get my behind into the car and see what it is like. I'm not so great with auto trannies, but if they replace the valve body, seems like they will be replacing the fluid as well. ?