I am trying to understand how the evap purge solenoid is controlled by the ECM. In my case we are talking a 2011 Wrangler JK, but I believe the system works similarly in many other vehicles.
I understand the the opening and closing of the solenoid is controlled by the ECM sending a ground signal.
I have a few specific questions related to this:
I have heard people say that the solenoid received "Constant Voltage." I am sure that the ground signal is not working between my ECM and the solenoid, but when I test the positive and "ground" coming from the ECM into the solenoid with a multimeter, I get around 12+ volts.
If there was no ground signal being sent, wouldn't it show zero?
If I replace the wire coming from the ECM to the solenoid with a wire connected to the negative post on the battery or any other ground wire, the solenoid works. I am able to command it to open using a scan tool and I can feel it, so I know it is working properly. My guess is, the solenoid is now going from always closed to always open, but I am not 100% sure. My guess is this is causing a P0443 because the valve is now always open compared to before when it was always closed.
If the positive cable from the ECM and the ground cable from the ECM are connected to the solenoid, it doesn't work even though testing these two cables with a multimeter shows around 12v to 13v. In this case, I am thinking the solenoid is always closed because the ground signal is never being sent properly from the ECM.
So, I am trying to understand why these wires from the ECM to the solenoid would be showing 12v to 13v if there was not a ground signal instead of zero.
Additionally, I am then trying to understand exactly what "switching ground" means. Is the system just sending power via the negative cable and then it switches it over to ground when it wants it open? Is the system otherwise sending voltage via both the positive AND negative cables until it switches to ground and that is why I get the 12v to 13v?