I have a 2005 Frieghtliner with a smart shift transmission. SM code comes on and my truck won't switch gears?

SOURCE: 1978 chevy k20 4x4 truck

try checking your vacume lines..

SOURCE: truck wont shift automatic. stays in 3rd gear. can shift manually

either repair or replace the transmission...sounds like the sensor went out

SOURCE: 88 s10 pickup truck will not shift from 3rd gear to overdrive

need more info i had a 1984 chevy half ton and first, second, and third worked fine but lock up didnt work. the problem was there was no vacum at a switch under the hood on the fire wall also your shift linkage could be out of adjustment. try driving down the road and raise up a little on the shifter.

SOURCE: transmission will shift, but car won't move.

there is a linkage inside the transmission that came off or lose so you might have to take it to a mechanic to get in there and repair so do not start car no more and you might have to have the car towed to a mechanic to look at it.

SOURCE: 04 SAAB 9-3 THREE CODES P1743, P0735, P0734, TRANSMISSION WON'T SHIFT

Could be that a sensor has failed.My suggestion would be have local shop scan it....Could be so many things.......