Hey guys
I'm new on this forum and your help would be apreciate
I bought a 2003 audi a4 and something just went wrong, everything was find but tonight, i had to use booster cables because my baterie was dead (let a door open and a aux plug). When i started my car, i did a small ride to let my battery charge. When i start it again a few hours later, my check engine was on and i really don't know why, there were no unusual sound and it freak me out a little. When i leave my car in my frontyard, they rad or something start by himself and it's pretty loud, like a fan sound, it's new and it's very scary. I always use Supreme gaz by the way and i heard that it could be the the gaz cap or a sensor. I don't want to pay an Audi garagist to do to job because it's very expensive as you know. I always had a sound of electric in my dash on the passenger side but i never had any problem with it. I have to mention that the hour and the time of my car came back to 2002 in January. So if one of you can help me with my issue it will be very appreciate!

Sorry for my english and i hope that you can help me
Peace
Gab Simard