DTC P1780: O/D Off Switch Circuit Shorted To Ground Or Open: Description
WARNING: This page is about a different car, the 2002 Mazda 626 and 2001 Mazda 626. However, it is still accessible from the selected car via links, so may be relevant.
DTC will set if PCM detects O/D OFF switch is not cycled during self-test, PCM determines that O/D OFF switch circuit has a malfunction.