I have a newly rebuilt transmission for a 2005 F250 6.0L truck with about 2000 miles on it since the rebuild. Recently the transmission started acting up a little. It starts with a hard shift, normally while driving in traffic or driving in the first few gears/shifting through them. After the hard shift, the tow/haul light starts flashing. Truck will continue to shift. However, if i come to a stop, I won't have 1st gear available so the truck is really slow to start moving forward particularly when i have to stop on a hill. The problem is intermittent and i haven't been able to observe a specific set of circumstances to cause the issue to surface. Except that its about 30 plus minutes into a drive, normally in traffic, and doesn't matter if i am driving up a hill or not.

Dealer took the truck in for a while, tested everything, couldn't replicate the problem, but read the same code that i found. They think it is an electrical problem but haven't been able to find any issues in the wiring harness.

As far as i can tell, the code is associated to the shift solenoid D circuit. Is this more indicative of a failing/faulty solenoid?

If the solenoid fails, can that cause any large problems in the transmission? I would rather not mess up the freshly rebuilt tranny. Thanks for the help

 

Since the shift solenoids control all shifting in the transmission, then yes, a faulty solenoid WILL cause large problems with the transmission. Depending on your code, it could be a bad solenoid, wiring, or both.