The only thing you can do is replace them with the correct ones or get JScan and delete the TPMS, that's what most of us do. Some Tire Stores maybe to delete the TPMS also if you decide to do that.
Do a compression test that will let you know if it needs replaced, if the headgasket leak isn't real bad try putting some of this sealer in the coolant.
https://www.amazon.com/K-Seal-ST3501-Permanent-Gasket-Repair/dp/B00QYZIVA6/?tag=jkforum-20
My JK's been like that for 3 years now, never scanned it to check Codes to see what it could be. I don't care for the ESP or ABS so just didn't worry about it, just figured it was a wheel speed sensor.
You shouldn't need the volts reading since you have one on your dash, so just unplug the power to the volts meter on the backside of the switch assembly.