Oh, awesome - that is very helpful. I did not think the ECU provided that level of voltage, and I was laboring under the delusion that current flowed from the voltage rail through the chassis of the device to ground, and somehow the ECU enabled that.
So if I understand you, the solenoid is held "neutral" by an equal and opposing voltage that prevents current flow. The ECU controls the solenoid by lowering voltage and allowing current to flow through the solenoid, activating it, using the ECU as a ground. I'm surprised that that kind of current can flow through the ECU!
Okay, now I know what I'm looking for, I just need to set up the right device to capture the data. Can't tell you how much I appreciate your input, thank you again.