When must you check the level of the brake fluid?

The illumination or failure to extinguish of the braking system warning light is a signal of a possible malfunction, most commonly related to the brake fluid level being too low. A low level of this fluid constitutes a critical safety hazard, as it can lead to a significant reduction or a complete loss of braking effectiveness. Therefore, it is the driver's responsibility to immediately check its level in the reservoir, such as the one visible in the picture.