Don't put 12 volts on the solenoid.
Check continuity between solenoid (at unplugged wire on solenoid side) and chasis ground. Should have 14 to 30 ohms. If not, it's the solenoid.
Check continutity between A4 at the ecu and green and white (or whatever color it may be) that plugs into the solenoid. If nothing, you have a wire problem between ecu and solenoid.