Kenwood 5140 won't dim

[Will B]

I know this is a Pioneer forum but I'm hoping some one here can give me a hand. I've had the 5140 installed in my 04 Chevy truck from about 4 or 5 months now and it's worked great. A couple weeks ago I had some custom tuning done to the motor in my truck. We had to pull the radio fuse under the hood when we flashed the trucks computer. Ever since then I can't get the head unit to dim when the head lights come on. It will dim if I go into the monitor section and turn Dim on but before it would just automatically do it It won't dim when the Nav-Sync button or the Sync button is pushed and the headlights come on. Any help?