The solenoid is certainly part of the circuit. If the solenoid has developped an internal open/short to ground then it will need to be replaced. Test it by putting an ohmmeter on it and see if there is continuity through the solenoid and no short to ground. Because there are a few inches of wire between the transmission connector and the solenoids themselves, you'll ultimately have to drop the transmission pan to be absolutely sure that the fault is in the solenoid. PErsonally, I would verify the external wiring first, then drop the pan to check the internal wiring.