No acceleration, "Service Transmission" message C30 T5
 

Recently bought a 140k miles, 2012 C30 T5, automatic.Taking off from stoplight a few days ago, car suddenly had no power, maybe in limp mode? RPMs did not increase, even with pedal to floor. Stopped in next parking lot. Message said service transmission. After 5-10 mins, I cranked it again. Message was gone, drove normal. Any ideas where to start? Dealer wants $130 to hook up to scanner to diagnose. Thanks!