Why does my engine cuts of when temperature fans comes on

You may have overheated the engine. Stop car let it cool for several minutes or hours if possible. Check coolant overflow reservoir and if accessible AND SAFE locate and using a gloved hand or shop rags remove radiator cap. Make sure coolant is full and topped off with proper Coolant Mixture NOT JUST WATER! Many times people assume that since Plastic Reservoir appears full that Radiator must be Full too however especially in higher mileage vehicles Corrosion and foreign objects can occur and cause blockage in the hose that attaches to top of radiator near cap. Be sure to replace or at least inspect and clear then tighten this hose once fluids are topped off. Then cross your fingers try and start then run car and see if fans come on again or if engine shuts off…if so you may have more serious problem like warped or blown head or intake manifold gasket …valve body or engine head damage also possible if you continued to drive vehicle while running hot which is NEVER RECOMMEND unless absolutely necessary to personal safety.