A very small fixed current is passed through the coil of a solenoid during use thereof when the solenoid is in its “off” state of cyclic PWM command, the fixed current being less than the current required to actuate the solenoid to the “on” position. While the current is flowing through the coil, the voltage across the coil is measured. The resistance of the coil is calculated according to Ohm's Law. When the actual resistance is known, the duty cycle imposed on the solenoid may be altered to compensate for the resistance deviation from nominal. This allows, for example, fuel injectors for internal combustion engines to deliver the correct amount of fuel under all operating conditions.