This codes refers to the 1-2 shift solenoid. Be sure to check all fuses first. Specifically the
"TCC" fuse in the underhood fuse block.

If that is ok, 2 things possible. Either you have a connector problem at the 20-way
transmission case connector causing this code, or the solenoid. The solenoid is on the
valve body in the side case of the trans.
Suggest disconnecting trans. connector with key off, look at all terminal, pull the harness
a little so as to change its position, then plug it back in. Clear the codes and drive it.