occasional lurch, automatic downshifting 5>4

[dai]

Help: hard shift while in automatic, downshifting 5>4

2012 LTZ hatchback, 58k mi

this has been a little bugger that usually surfaces, as far as I can tell, when it's damp outside. It'll happen in the morning when there's dew on everything in the spring or sometimes fall, and has happened ever since a few weeks after I bought the car new (oct '12). Quite simply, when slowing down, it will shift from 5th gear to 4th around 30mph and thud. No other gears do this or stall during shifts, going up or down, including 4th to 5th.

I complained to my dealer several times before my main warranty ended, but was unable to reproduce the problem because the issue always managed to vanish by the time I'd managed to drive more than a few miles, and not show back up for a long while.

This past week it returned, and while that does line up with the weather being extremely wet and foggy (chicago's suddenly in springtime), it hasn't stopped doing it reliably every time it shifts down now, for the past 4 days. I've been countering this by using manual or coasting in neutral as I'm decelerating, and plan on hitting a shop extremely soon. Is there something obvious here I can do about this, or direct the mechanic towards so they don't waste time on trial/error? I understand the thud/lurch itself is the a physicaltransmission, but could this be some weird electronics issue that's affecting when the car thinks it needs to shift?

The car is right on the brink of needing an oil change, but I'd assume that's not linked. other than that, no warnings on dash, and no error codes in torque.

 

[Greg4412]

I bought my Sonic used with 31000 on it 1.8 auto LT.hatchback. it has always shifted rough since I have had it upshifts and when downshifting it seems to keep the engine rpm high and doesn't coast like all the older autos do. I removed the abs fuse to disable the traction control because I personally don't like it. The transmission upshifting is smooth no jerkyness and it coasts now more when you let off the accelerator.
I think it's the traction control of the stabilitrack systems causing this. I replace the fuse for the traction control and it returned. Jerky shifting ect ect. I replace the fuse in the winter because one of the drawbacks is it you loose abs brakes and there is no brake balance. Braking seems to be 50% front 50% rear with this fuse removed.
Gm needs to get rid of these for front wheel drive cars why does a front wheel drive need traction control. All the weight of a front wheel drive is over the drive tires.

 

[Chevrolet Customer Care]

I bought my Sonic used with 31000 on it 1.8 auto LT.hatchback. it has always shifted rough since I have had it upshifts and when downshifting it seems to keep the engine rpm high and doesn't coast like all the older autos do. I removed the abs fuse to disable the traction control because I personally don't like it. The transmission upshifting is smooth no jerkyness and it coasts now more when you let off the accelerator.
I think it's the traction control of the stabilitrack systems causing this. I replace the fuse for the traction control and it returned. Jerky shifting ect ect. I replace the fuse in the winter because one of the drawbacks is it you loose abs brakes and there is no brake balance. Braking seems to be 50% front 50% rear with this fuse removed.
Gm needs to get rid of these for front wheel drive cars why does a front wheel drive need traction control. All the weight of a front wheel drive is over the drive tires.

We appreciate your feedback, Greg4412. We'll be sure to note your concerns for future product consideration. If you have any further questions we're happy to do what we can to help, or we'll reach out to your local Chevy dealer for additional technical support. Thanks for your time!

Amber N.
Chevrolet Customer Care

 

[MidnightClub3]

I have the same problem minus the thud. Fifth to fourth (at 27 mph) is rough every time. The lurch can definitely be felt in my seat I just hope it doesn't progress into something worse.