A vehicle includes an engine, a transmission, and a controller which executes a method. The transmission includes a clutch having an actuator which applies the clutch using position-based control logic. The transmission also includes a fluid pump and a variable-force or other solenoid valve positioned downstream of the pump and upstream of the clutch. The valve outputs a flow rate (Q) for a corresponding solenoid control current (I). The controller adapts a calibrated Q vs. I characteristic table of the valve for different transmission temperatures by applying closed-loop position control signals to the actuator at the different transmission temperatures and recording a null point(s) describing the corresponding solenoid control current (I) at a zero flow rate condition. The controller calculates an offset value for solenoid control current (I) using the recorded null point(s), applies the offset value to the characteristic table, and controls the clutch using the adapted characteristic table.