Service Trailer Brake System light came on without towing on 2007 GMC Sierra 3500 HD

The servcie trailer brake system light just came on and i'm not towing anything.

Asked by for the 2007 GMC Sierra 3500 HD
turn on the off tow haul mode on end of shifter
that all i have to do and the light will go off,the truck is a 2010 gmc sierra 2500 hd