I am working on a 00 Cadilac SLS, and the tranny shifts fine up until 4th gear will not go into 4th. I pulled codes P0741, P1639, P1845, P1860. I know what P0741 is (TCC Performance or Stuck Off) but not so much about the other codes or even what would cause them. Any ideas on the cause and the fix would be great.
Thanks
Joe

Pressure Control Solenoid would be my choice, controls line pressure in transmission.