::Bumpin' like it's 2001::
It's been a while since my OP but I took a while to isolate the issue. When the T/C light would throw, there was no code stored in history - but P0106 was activated with the light.
I didn't feel anything, but I was also racking up some misfires in a couple of cylinders. I learned not to feather the throttle and avoided accelerating too hard, and it didn't recur often so I left it alone for a while to see if it would sort itself out.
In the meanwhile, the stainless flex downpipe from the exhaust manifold rotted out and - guess what? - that's an integral part of the catalytic converter. That cost me $600 in P+L to fix. Thank you, nameless GM engineer.
Within a few days after fixing, my check engine light came on a few times. It would typically occur at high speed (65-70 mph) while cruise controlling down the freeway. Code was P1174 (air:fuel mixture imbalance between cylinders). It would clear after 3 ignition cycles and wouldn't come back for a while, but it did persist 3-4x before I made it into my Chevy dealer.
<Backstory: this dealer replaced all of my fuel injectors 10 months and 15,000 miles prior. The SES light had come on and, guess what... it was P1174. $650 later...>
The fix: updated ECM calibration data from GM - a reflash for the computer. Cost $95. As the car wears, performance parameters and the interaction of all the systems changes. The manufacturer attempts to compensate for this in their system model, but often they miss the mark. My car was mechanically perfect, but was throwing the check engine light and driving very stupidly because the model was probably running some cylinders lean (who knows what else). You get a new fuel map, etc.
End result: my car actually feels a heck of a lot newer than it did. Fuel economy is up 10-15%, shifts are much smoother, the throttle is much more responsive, and I honestly believe I may have gained up to 10 peak horsepower and definitely have more torque across the powerband. This car is fun to drive again. It was on a downhill slide for a year or two and I barely noticed/chalked it up to age. No more T/C lights or SES lights.
I would recommend checking into this if your Cobalt is aging, getting poor fuel economy (and it's not a typical suspect like air filter), or throwing the T/C light/exhibiting P1174. Ask your dealer if your car is a candidate for an ECM update. If I find a link to the appropriate bulletin, I will share.