Fluid ejection systems and methods thereof are disclosed in the present disclosure. The method includes establishing fluid communication between an ejection chamber and a fluid supply chamber of the fluid ejection system such that the ejection chamber includes a nozzle and an ejection member to selectively eject the fluid through the nozzle. The method also includes detecting at feast one impedance in the fluid by a sensor unit haying a sensor plate, and identifying the characteristic of the fluid by a fluid identification module based on the at least one detected impedance value to obtain an identified fluid characteristic.