Pseudoelastic Co-Ni-Ga high-temperature shape memory alloys are characterized by a wide range of tunable transformation temperatures and lower processing costs compared to conventional Ni-Ti-X HT-SMA which renders them useful for high-temperature applications in automotive and aerospace industries. In recent studies the fatigue behavior of Co-Ni-Ga single crystals was analysed by TEM and neutron diffraction. It was revealed that functional fatigue is dependent on two processes: increasing defect density and chemical ordering of Co, Ni and Ga. However, two temperature dependent aspects of fatigue behavior remain to be clarified: martensite variant selection under tensile and compressive load and elastic constants of both austenite and martensite. In situ neutron single crystal diffraction is our technique of choice as it allows to reliably investigate both aspects at the same time.