Thanks, I will look because it is in fact the front truck that is not working.
If your model is the newer one with two motors, the front motor may have stopped working due to a loose wire. Take the shell off and watch the front motor drive shaft as it runs. If the shaft does not turn, the motor is not running and you then need to check the wiring. If it appears that the motor is running but the truck still is not turning, the drive shaft may be broken or loose.
I have a brand new DD40 with sound and it is giving me some trouble. The sound, lights, etc... all are working fine, but it all of a sudden quit pulling any cars or essentially itself. It looks to me as thought the front set of trucks has quit working, has anyone had a similar problem? What else could it be and how do I go about fixing it? Thanks for any help!