The EVSE can be sensitive to noise on the ground wire of the circuit but in this case you should check all of the outlets, junction boxes and fixtures in the detached garage:
"In many cases the open ground on one outlet is the result of a disconnected wire at another outlet. A wire disconnected from one outlet will disconnect the ground service from all the outlets down line."
I get a Power Fault indication light on my Level II EVSE whenever I use my plug-in leaf blower. The blower motor adds sufficient noise on the ground line that the EVSE picks this up as a ground fault. It does not matter what outlet or circuit I use with the blower, always get a fault on the EVSE. The fault clears automatically in about 20 minutes after I finish using the leaf blower. I doubt your problem is noise on the ground line but you might leave the EVSE plugged in, not connected to the vehicle and see if the Power Fault lights clears after a while.
Always turn off the power when testing continuity of the wiring and the outlet. It could also be a neutral wire crossed with a hot wire or even a hot ground (very dangerous.) I would get an electrician to find and fix the problem.
"In many cases the open ground on one outlet is the result of a disconnected wire at another outlet. A wire disconnected from one outlet will disconnect the ground service from all the outlets down line."
I get a Power Fault indication light on my Level II EVSE whenever I use my plug-in leaf blower. The blower motor adds sufficient noise on the ground line that the EVSE picks this up as a ground fault. It does not matter what outlet or circuit I use with the blower, always get a fault on the EVSE. The fault clears automatically in about 20 minutes after I finish using the leaf blower. I doubt your problem is noise on the ground line but you might leave the EVSE plugged in, not connected to the vehicle and see if the Power Fault lights clears after a while.
Always turn off the power when testing continuity of the wiring and the outlet. It could also be a neutral wire crossed with a hot wire or even a hot ground (very dangerous.) I would get an electrician to find and fix the problem.
