Pub. Util. Code, § 736

All complaints for damages resulting from the violation of any of the provisions of Sections 494 or 532 shall either be filed with the commission, or, where concurrent jurisdiction of the cause of action is vested in the courts of this state, in any court of competent jurisdiction within three years from the time the cause of action accrues, and not after. If claim for the asserted damages has been presented in writing to the public utility concerned within the period of three years, the period shall be extended to include six months from the date notice in writing is given by the public utility to the claimant of the disallowance of the claim, or of any part or parts thereof specified in the notice.

Whenever the commission institutes an investigation of unauthorized undercharge by any public utility, the institution of the investigation by the commission shall toll the three-year period specified in this section until the commission has rendered its initial decision on the matter. The commission shall render its final decision within two years of the date of the order instituting the investigation.