I posted this reply earlier to a similar OP query.
I had a similar problem with my 04 Concord. It would randomly go into limp-home mode at the 1-2 shift. Pulling over and turning off the engine for a few moments would reset the computer and all was well again… till the next time. The CEL was indicating improper shift servos operation (don’t remember the code). Dealer replaced the servos twice, but no help. Dealer finally resolved the problem by re-flashing the computer with updated software. Hope this helps.