You can quickly and accurately assess the condition of the DOT3, DOT4 or DOT5.1 brake fluid in your vehicle with this simple, effective brake fluid tester pen. 5 LED indicator lights let you know how much water content is in your brake fluid so you can determine when it's time to change the fluid. This pocket-sized tester comes complete with a AAA battery and cap to protect the testing prong How to Use: 1. Turn on the brake fluid tester by pressing the button on top. A green light should light up. If the light does not come on, it may be time to change a battery 2. Unscrew the lid for the brake fluid reservoir, and take off the cap for the brake fluid tester 3. Dip the test probes into the brake fluid and the LED lights will indicate the percentage of water in the brake fluid 4. After testing, remember to screw the lid of the brake fluid reservoir back on tightly 5. The tester will automatically power off after 12 seconds of inactivity What to Do: The LED lights will indicate the percentage of water in the brake fluid: -Green: No water - Green/Yellow: Less than 1% of water - Green /Yellow/Yellow: Approx.2% of water - Green/Yellow/Yellow/Red: Approx.3% (Brake fluid should be changed) -Green/Yellow/Yellow/Red/Red: Approx.4% (Brake fluid must be changed urgently!) Please Note: The brake fluid tester is calibrated for DOT4 and DOT3 brake fluids, and DOT4 is used in most cars produced since 2006 Replace the battery if the green LED indicator no longer lights up after you press the button Wash the test probe with tap water after every use In case of skin contact with brake fluid, thoroughly wash the affected skin or clothing with water Do not expose brake fluid to the atmosphere for a long time as it is highly hygroscopic Package： 1 x brake fluid tester(Battery Not Included)