VMF, UCF, I have a good news for you. This morning when I started the car, the volume works as good as before. I don't know how long it will stay good. However, I still like to figure out what caused the problem in the beginning. I found this link on the web. Check it out. I tried to look for the connector they described but I can't find it. Thank you all of you who's trying to help me.
http://carstereohelp.com/repairDoItYoursel...usRepairVol.htm