Eaglerich Original Pack Mini Electronic Brake Fluid Liquid Tester Pen Auto 5 LED Car Vehicle Tools Diagnostic Tools Universal the green LED lights = water content in the brake fluid H2O &lt;1.5%, brake fluid qualified the yellow LED lights = brake fluid water content H2O = 1.5% to 3%, can continue to use, test again six months later the red LED lights = water content in the brake fluid H2O&gt; 3%, can not continue to use the brake fluid needs to be replaced Red LED: change brake fluid LED red flashing: battery replacement LED yellow: low moisture content, check again in six months