Can I power up the ECM without an engine attached?

[kipps]

Based on my schematics, the run/crank relay provides an ignition hot source to the ecm. The ecm in turn, activates the powertrain relay, which "turns on" the engine sensors and components. I want to know if the ecm will automatically power up that relay when it gets a key on signal, as does it need a data signal to do so.

If you didn't follow that mumble-jumble, don't sweat it. On to the question...

Can I provide 12 volts to the appropriate pins on the ecm, and read the output voltages on various pins without an engine attached? Or is this somehow dangerous or ill advised?

I would be doing this through the stock harness and fusebox. So I won't be just blindly pushing alligator clips into the ecm pins...