I have posted before about my brake pedal no returning all the way or slowly returning which is was a intermittent problem. the pedal last inch of its throw would stay down draging the brakes a little or would return slowly. some days it would not happen and some days it would happen 20 times or so. I usually put on 100KMs a day with the car for work related business. I put on 5000KM in one month with work/personal KMs once but 2500 to 3500 KM is the usual amount. I discovered the problem around 3000KMs and it was appears to be resolved at 12,834 KMs.
I visited the dealer twice regarding it with the second visit being turned away and told they will charge me for a full brake inspection if they do not find anything wrong.
At this point I spoke with the operations manager regarding my problem. She saw things as my problem is her problem and she believed it was still there.
on my third visit the car was left for two days.
1st day for a complete inspection (no threat of charges) calls with GM and finally a decision of the cause of the problem - Brake booster check valve intermittantly sticking causing slow release of brake pedal. plan - replace brake booster. Part was ordered.
2nd day - brake booster replaced. procedure - removed air inlet duct, under hood fuse box, and brake master cylinder to gain access to brake booster. Brake vacuum booster replaced and reinstall of other removed components. Brake pedal pivot was checked and found no signs of binding at this time.
Booster 048050 Part # 15261541 Replaced under warranty
at 12,843KMs on 05 Cobalt SS supercharged.
IF you have this problem you may PM me in order to gain support from your GM dealer.