My car started right up one day for a couple of seconds then stalled. Ecu blinked 16 times I changed the relay still won't start. The ecu only does the hello blink and stays off.

Perform tests, in Honda Sections 1 and 2, below:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563.html

Remember to reset the ECM by disconnecting the negative battery cable for 10 seconds.