car brake fluid tester auto diagnostic tools 5 leds testing accurate oil quality digital vehicle automotive test

brake fluid detection pen is based on the change in conductivity to determine the moisture change brake fluid. it shows clearly the extent of moisture contained by the light-emitting diode, high moisture content will lead to lower boiling point, affect braking performance. red indicates the brake fluid needs immediate replacement, green represents good condition, yellow indicates the state is acceptable but soon replaced.press the switch to turn on the power, the green led light that represents the battery properly, the green light does not shine on behalf to replace the battery