Trying to build a small GSM library

Yes, I had a feeling that digitalPulse(C0,1,2000); may not have been quite right.

The best thing is probably just to replace it altogether:

digitalWrite(C0,1);
setTimeout(function() {
  digitalWrite(C0,0);
  Send_Command(...)
}, 2000);

Of course you might need to wait a few ms after taking C0 low again too...