dicer

The first thing to do is back trace the wiring from the OBD plug to the ecu and make sure the connections are good.
Does the check engine light come on just before starting the engine? If not the bulb could be burned out.
A bad catalytic converter will NOT causes a no communication issue, the only electric connection a cat has is the O2 sensor down stream from it.
And anything wrong there will show a code and possibly illuminate the check engine light. It could be the ecu capacitor issue as mentioned above.