Methane is the energy source of a car and it is registered in the registration certificate as other energy sources. The same rules apply to it as to other energy sources. Methane fuel tanks are so-called pressure tanks and are inspected in regular inspections and it is recommended that professionals have them checked regularly during the life of the vehicle. It is allowed to stop using a methane system that was installed as a aftermarket system (valid only in those cases). But then the equipment (at least the pressure cylinders) must be removed and the car brought to a modification inspection to have methane removed as an energy source from the registration certificate.