Brake Fluid TesterCheck Fluid Quality: Press the button for power on, green LED will light up. Insert the tester into reservoir for a second , then the results will be indicated correctly by LEDs. Auto power off . Indications: Green: Battery OK, i. e.: No Water Contained in the Brake FluidYellow: Less than 1% of Water Content in Brake FluidYellow Yellow: Approximately 2% of Water Content in Brake FluidYellow Yellow Red: Approximately 3% of Water Content in Brake Fluid;