Hey fellers, first time poster here. Awesome forum! Here's the problem I'm hoping one of you G-ru's have heard of: 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. Basically the engine goes: Rrrr...Rrrr...Rrrr and the tach bounces until I change throttle position.

 

I believe there is a TSB for this...take it to your dealer, they might have a reflash.

 

Cool, thanks. Thing is, I hate to go to the dealer w/out at least having the TSB# or a printout of it. I'd just get the blank stare of the "could not duplicate concern".

 

A guy on another forum took his 2007 2.2L, auto to his dealer for the exact same issue. No TSB's and they can't duplicate the concern. He's had it in several times. Any ideas? Bueller?.... Beuller?

Thanks man

 

same issue here, no fix that i know of, though it is annoying...Ive learned to just accelerate a little harder.

 

I have the same problem and took it to the dealer and same results can't duplicate problem. They went ahead and reflashed the pcm and that did not change anything. I was told by the dealer that until the problem gets worse or it throws a CEL that they could not fix it.

 

Thanks guyz. Best we can do from here is keep this post alive and hope GM Goodwrench sees enough of this problem to find a solution. I've also learned to either ease off the gas or get on it harder to stop the surging. I think I've isolated mine to being the torque converter trying to lock, but instead it surges in/out of lockup on mild accelleration and upshift. I know the 4T45E has "pulse width modulated" torque converter locking as opposed to an on/off solenoid (lots of ATs do now). Being PWM, it's kind of like having a linear actuator for the TC lock. It's there to soften the feel of the TC locking. Honestly I think the problem lies there somewhere with the 2007's, problem is, 2005 and 2006's have the same trans. I'm guessing it's a software as opposed to a hardware problem. Dunno man!

Joel

 

I know some fullsize trucks suffer from the same issue (99-01 Sierra's)

 

I think the problem with it, as i have been purposely trying to do it, is under light accel. we confuse the computer as we are right at the border between the two values, so it jumps back and forth, i think the only thing to do really is to just accel. harder, or let off. GM can change the value it looks for, but it would just change where the tach jumps at....

 

My girlfriend's '07 2.2 auto does the exact same thing. We've had it to the dealership twice and both times were told that they could not duplicate the problem and could not do anything unless it throws a code. They reflashed the PCM, but that did nothng to solve the problem. It seems worse when the outside temp is cold (about 40 and under). Kenny Ross Chevy in Irwin, PA seems to know nothing about it... if anyone hears anything on any service info or TSB's, please shoot me a PM.

 

Update... we just had the '07 in the shop again, this time at a different dealer. The tech went for a ride with me driving, he saw and felt the RPM surges. They kept the car overnight, tech called GM engineering and found that they ARE aware of the problem, and just issued a TSB on January 11. Engineering is working on a permanent fix for the problem. In the meantime, they cleared the "learning" portion of the transmission control, in other words reset it to brand-new. This temporary fix may only last a couple hundred miles, but GM IS working on a solution and will issue instructions to the dealers when they have it. Keep in mind, the more cases that are opened with GM, the sooner they'll create a solution.

 

Sweet! Thanks for the update. Any chance at getting the TSB#? I'd like to be armed with at least that for my knucklehead dealership. I'm at 10Kmi with 2007 2.2L, auto and she still does the RRRrrr.....RRRrrr....RRrrr jumping into lockup on light acceleration.

 

Well I have access to GM Dealerworld website and searched all over for any TSBs regarding this issue. Couldn't find it, so presently there is no correction. I keep an eye on all the latest ones, especially pertaining to cobalts so I'll let you know if something comes up.

 

I appreciate that RS75-. My '07 has been rock solid aside from this occasional RPM bounce that irritates the hell out of me. There's maybe 3-4 2007 (2.2 auto) owners now that I've read about that have this issue. One owner on another board claims his dealer did a software reflash that fixed his. Others say the reflash did nothing?!? Who knows. All I know is the later 4T45Es have a pulse-width modulated torque converter lockup as opposed to an on/off solenoid. It's supposed to make TC lock undetectable. YEAH RIGHT!!

 

What the tech did was to call GM and get their solution from their engineering department. There presently are no TSB's out just yet, however they were told to clear the "shift adapts" in the transmission control module. It's been several hundred miles and her car is fine so far. According to them, they have to clear the shift adapts then drive the car for 30-40 miles immediately afterward. They told us there was a chance it could come back after 200 miles; however in our case it hasn't. Tell your dealer about this, suggest that they call GM and ask about this case. The dealer she actually bought her car from did nothing but reflash the PCM and that solved nothing. My dealership is actually the one who took the time to try and solve the problem, so if you can't get anywhere with your dealer, you might want to try finding one who is a little more willing to investigate the matter.

 

I'm finally going to drop it off at the dealership tonight. I'm just under 12Kmi and it's still doing the crazy torque converter lock bounce. We'll see what they can't find and try to charge me for!

Joel

 

The Techs were able to duplicate the concern. Apparently "GM Engineering" is aware of this issue effecting ~2007 2.2L 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.

 

That's what they did for us as well, glad you finally got some satisfaction out of them. We've put well over 1K on the car (probably 2K, actually) since then and it's been fine. She's now driving it to and from school every day (about a 30-mile round trip) and has had no problems, so hopefully we've seen the last of it. Keep us posted on how your car is doing.

 

I have a 2.4 2007 w/auto trans w/ 6,100 miles on it. I am experiencing exactly the same issue. If you apply heavy accelerator pressure- no problem. But, if you apply moderate pressure, like to pass someione on the highway, the tranny downshifts, the RPMs go to 4,000 and then it quickly drops 500 rpms-almost bogs down momentarily, but you can feel that its like going into overdrive mode. If you then apply a little more accelerator pressure it quickly shifts down again and will maintain higher revs untill you let off. I found that it is most annoying on a 3 hour drive along the 90 thruway in cruise control. I scheduled an appointment today for tomorrow morning and did my best to describe the issue to the service manager, but I plan on reiterating the explaination in the morning with whomever they assign to my car at the dealership. Has anyone gotten any further updates on GM's response or fix for the problem?

 

GM is currently working on a 'permanent' fix, but to my knowledge hasn't issued one yet. Take your car to the dealer and explain what has been said here- Engineering is aware of the problem and will explain to your dealer how to clear the adaptive shift logic and reset everything. My girlfriend's '07 was done right after I got my '08, so about 2 months ago, and hasn't shown any further problems yet.

 

Tman, I see you are from the Buffalo area as well. West-Herr Chevrolet is where I took mine (and purchased it). At least they are familiar with this issue. They put like 60miles on mine troubleshooting it. It should be quicker for the next customer. I was very impressed with their service writers and whole dept for that matter.

 

MTPockets,
Did you go to the Orchard Park one on Southwestern Blvd? Who was your serviceman? RED, Green or Blue Team? I'm assigned to Andy Elfman. I bought mine there as well from Erica Bieler.

 

Yep, that's the one. I bought mine from Matt C. My Service Adviser was Frank G. Not sure of the color though! This was my first service visit. Frank knows what's up with this issue, but I'm sure they'll have to 'diagnose' yours first. I was sweating having to shell out for a diagnostic fee like they normally try to get you. No mention of anything, no charge what so ever.

 

OK, so I dropped my 2.4 auto Cobalt off this moring. The serviceman ( Andy Elfman) knew what I was talking about when I explained the shift logic in the TCM is not functioning properly. He also very abruptly informed me that there is no current fix for the problem and of course the engineers at GM are working on it. I told him that others with the same problem have reported that their dealer disabled the shift logic and reset the TCM. He informs me that that fix has proved to be only temporary and that that solution has been abandoned. He is having the logic cleared of what it has learned of my driving habits, but claims that the flutter will return. Apparently we all have to wait for a permanent fix. He informed me that the engineers are rewriting the logarithms envolved in the computer control. In my experience with GM priority, the more complaints reported to them by dealerships, the more attention they pay to expediting the fix. Safety issues come first for obvious reasons, then the problems with the greatest number of incidents. So, I encourage everyone with this issue, which probably effects many Cobalt drivers, but goes unrecognized by many, to make an appointment and report this problem. I hope that by posting this it will make others more aware and cause them to look for it.

 

Here's a little something you guys can try. It's won't fix the problem, but it will show you how your converters lock and unlock. There are two very normal things that will cause your converter to unlock. The first is completely coming off the gas pedal. The other is applying the brake. Try this and watch what happens. Don't worry, it's perfectly ok for the car.

While cruising at a steady speed with a steady RPM, keep your right foot on the gas wherever you have it to keep your current speed. Then with your left foot, just touch the brake enough to basically turn the brake lights on. This will send the signal to the TC to unlock. But because you have your other foot still on the gas, the RPM's will suddenly rise. Take you foot off the brake and the TC will lock back up again.

Its a handy little demostration of the actual effect of TC lockup.