A vehicle system provides an excitation signal to an electrochemical system for use in Electrochemical Impedance Spectroscopy diagnostics. The electrochemical system is connectable to the vehicle system and the vehicle system includes a power stage, such as a charger, connectable to the electrochemical system for supplying electrical energy to the electrochemical system, and/or connectable to the electro-chemical system for withdrawing electrical energy from the electrochemical system, and an Excitation Generation Unit comprised by the power stage or operatively connected to the power stage. The Excitation Generation Unit is adapted for instructing the power stage to generate an excitation signal for use in the Electrochemical Impedance Spectroscopy diagnostics, and the power stage is adapted for generating the excitation signal and supplying the excitation signal to the electrochemical system when so instructed by the Excitation Generation Unit. A method provides an excitation signal to an electrochemical system using the vehicle system.