ITEM NAME:Brake Fluid Tester Electronic Pen For Multibrand Car For Dot3/4/5 Car Diagn K2A3 Brake Fluid Tester Electronic Pen For Multibrand Car For Dot3/4/5 Car Diagn K2A3 Brake fluid detection pen is based on a change in conductivity to determine the humidity change the brake fluid. This clearly shows the degree of moisture contained in the LED, a high moisture content will lead to a lower boiling point, affect the braking efficiency. Red indicates the brake fluid needs urgent replacement, green color symbolizes good.Press the button to turn on, the green LED will light up.Insert the tester into the tank for a second, then the results will be indicated correctly using the LEDs. green LED = water content in brake fluid H2O Less than 1.5%, brake fluid qualified.