Just joined to share a surprising observation I had with my sonata hybrid, a 2011 model I bought last August, now with 6k miles. I mostly drive it half local and half highway and road around my home is hilly. The gas mileage was about 30mpg before the October update, but after the October update it jumped to over 40 and car ran much more smoothly. After several weeks later had the November update and mpg dived immediately to 32. I was sure that something was wrong with the update, and a few weeks later contacted the service center who did the update and asked to do something. I was suspecting the computer in the car was somehow corrupted and asked them to factory reset the computer. Here I was invoking my experience with updating a smartphone. Even with a clean firmware update sometimes the phone does not work correctly and factory reseting solves the problem. The manager however said that the car is normal and the dip in mpg can be caused by temperature drop, and can do nothing for the car. Disappointed, contacted Hyundai America and reported the problem. A week later was told that it can do nothing but suggest I should go back to the service center or take my car to other service center for a check. Contacted the service center again and asked to redo the recall updates. This time the manager agreed and the update was done again a week later. With the update the car behaved better and mpg went up to 35. I was running the car this way for some time but was not completely happy. Then comes this surprise. Last sunday morning I decided to play with the Blue drive button and see what a difference in mpg the blue drive would make. So I turned off the blue drive and drove a few local miles. Surprise! Mpg shot up to 48. Incredulous, reset the mpg gauge and went to highway and drove 20 miles. Round trip mpg 43. Obviously there must be something wrong with the car computer. The blue mode in my car seems to be actually the normal mode, and vice versa. The car still runs well and averages over 40 with blue mode off. I guess Hyundai has still something to figure out to push the hybrid to its full potential. By the way temperature here hovers around 32F and my sonata is garaged in a heated space.