2004 dodge neon wont shift out of 1st

Hello, if the (automatic?) transmission will not shift out of first gear, then there is likely some kind of mechanical or electrical issue that needs to be resolved. Unfortunately, it will require hands on testing to get to the bottom of your concern.

Its possibly the wiring harness to the output sensor, the output sensor itself or the wiring harness that goes to the transmission has gotten wet and needs cleaned and dried.