(1) Whenever the commission believes that any rate or charge may be unreasonable or unjustly discriminatory, that any service is inadequate, or that an investigation of any matter relating to any public utility should for any reason be made, it may on its own motion and with or without notice, make a preliminary investigation.
(2) If, after making the preliminary investigation, the commission believes that sufficient grounds exist to justify a formal investigation of and hearing on the matters preliminarily investigated, it shall make an order to that effect.
(3) Thereupon, proceedings shall be had, conducted, and concluded in reference to the matters in like manner as though complaint had been filed with the commission.