1656 - It's a code for auto tranny problem but, for your swap it should be the TCS system
With the Acura ECU, the VCS in the Acura ECU is not compatible with the Accord TCS system. So, there is a conflict. Your TCS light should be on now, correct?
If this is the case; There is no fix for it, it will always be there.
If you have a CEL, that is maybe from code 1607 which is PCM error.
for your swap, most likely immobilizer.