Case 1: ibutton authorization is done after ignition ON
When the ignition is OFF, DOUT is 0.
When you turn ON ignition, DOUT becomes 1.
After ibutton authorization DOUT becomes 0 and the car starts.
Case 2: ibutton authorization is done before ignition ON
When the ignition is OFF, DOUT is 0.
As you do ibutton authorization it remains 0.
After ignition turn ON, DOUT is 1.
And the car will not start as long as DOUT is 1.
So, ibutton authorization works ONLY when the ignition is on.