Sorry, I only joined the thread part way through.

Generally the FAILSAFE message is flagged by the ECU when it detects an unexpected speed difference across the turbine & output speed sensors i.e. it is protecting the transmission from uncontrolled clutch slip. Obviously in Park and Neutral none of the clutches are applied (well, actually the F-brake is, but let’s not let the facts get in the way of a good argument) so there’s no slip to detect i.e. the transmission output speed is zero and the turbine speed is equal to engine speed as the torque converter isn’t loaded.

Your fault therefore sounds electrical. So you aren’t getting a P0705 error from the inhibitor switch? Did the error seem to be flagged by the actual movement of the gear lever?

Phil