Major RPM bounce 2007 2.2L, 4T45E

[JTK]

Anyone else ever experience a flutter or RPM bounce when the transaxle shifts into 4th during moderate acceleration? This is on my 2007 2.2L, 4T45E equipped Cobalt. It seems to only happen once fully warmed and I'm not positive if it's happening on the 3-4 upshift or during torque converter lockup in 4th? There is no check engine light and other than that, it runs flawlessly and has been perfect. I have heard of one or two other 2007 Cobalt owners with the same concern. No issue was found by their respective dealership service depts. I'm also not exactly sure if this is a throttle by wire problem, transmission problem, etc.. Basically the tach will bounce up/down about 500RPMs at about half second cycle during what feels like the 3-4 shift. You can hear it and feel it as well. Bad news is, it doesn't do it every time.

I know what I'll get if I take it in. It's been doing this off/on for about the last 2Kmi. Only 6Kmi total on the ticker.

Joel

 

[JTK]

For a little clarification on this, basically the engine goes: Rrrr...Rrrr...Rrrr.. and the tach bounces ~500rpms until I change throttle position. Then it settles right out.

Joel

 

[The Critic]

Sounds like a transmission flare to me. Keep a video camera in your car at all times and record the next time it occurs. Or every time it occurs if possible.

 

[meep]

agree. that's a gr8 idea. if you get the video you can take that to the dealer.... get it on record while it's on warranty.

M

 

[JTK]

Thanks guys, not a bad idea. Problem is, if the service dept cant duplicate the concern, there's nothing they can do. A member on another site I posted my problem at thought there may have been a TSB issued for this. I'd like to keep at it until I can get a copy of the TSB. Due to past experiences, I have little faith in my local Goodwrench service depts.

Joel

 

[JTK]

Just an update; I'm just under 12Kmi now and the torque converter oscillating in/out of lockup issue still exists, so I finally made an appointment and dropped the Cobalt off at the dealer. They had it for the day and drove it quite a bit. Their Techs were able to duplicate the concern. Apparently "GM Engineering" is aware of this issue effecting ~2007 Cobalts with the 4T45E AT. GM says it's a software problem that they are still working to debug. The service writer admitted it was way over his head, but it had to do with "serial bus #1, module 8" (something like that). In the meantime, what they did for me was download the latest software to my PCM and cleared the adaptive shift logic that the trans learned itself into. For now the problem is gone. It glides into lockup nicely w/out oscillating in/out. No cost to me and I was actually very impressed with how I was treated by this GM dealership. Basically the conclusion was; If the problem comes back, call them to see if the latest/greatest software is available. They will clear the shift adapts for me until a patch has been established.

Joel