To replenish the amount of liquid in the tank, you must remove the cap and fill in the liquid.
If you have to add fluid frequently, and a low level is signaled by a light on the instrument panel, then the brake pads may be worn out. The brake pads on the front wheels usually wear out.
Brake fluid - replacement
Brake fluid should be changed every two years or at 60,000 km. Brake fluid is a mixture of ethylene glycol, polyester oxyethylene and some other ingredients. This colorless or yellowish liquid is poisonous and also aggressive to paintwork. It does not attack metal and rubber parts and retains sufficient fluidity even at -40°C. Its boiling point is also quite high - about 290°C.
However, brake fluid is hygroscopic and «absorbs» moisture, which simultaneously lowers its boiling point. With a moisture content of 2.5%, the boiling point is only 150°C. This is quite dangerous, given that the brakes are subjected to significant stress. Moisture in such cases evaporates, forming air pockets in the hoses and pipelines of the brake system. The brake pedal in such cases fails and the brakes do not work. In this case, the only way out is to repeatedly press the brake pedal (pumping).
15. Take the brake fluid out of the reservoir, leaving a layer of fluid about 1 cm thick in it.
16. Fill with fresh brake fluid (DOT 3 or 4).
17. Unscrew the bleeding fittings on the brake mechanisms of the wheels one by one and bleed the system, each time making at least 10 full pressures on the brake pedal.
18. Monitor the level of brake fluid in the reservoir and top up if necessary, so that the reservoir is not empty and air is not pumped into the system.
Start bleeding from the fitting of the brake mechanism of the right rear wheel.