Transmission problem + "ETS OFF" and "Check Engine" are ON

I have 97' Chevy Cavalier 2.4L with Automatic transmission. Yesterday while driving 25-30 mph I felt like my car was hit in the rear but apparently it happened while transmission was switching gears. Before that moment transmission was really smooth and now every time its switching gears it does it with a real hit. Also "ETS OFF" and "Check Engine" lights came on. Please help to identify the problem. Thank you.