There are specific recommended intervals for engine oil change and, often, also for transmission and coolant change. But there does not seem to be any clear guidelines for brake fluid change. Do I need to change or replenish this fluid? This is indeed an aspect of car maintenance that is usually forgotten. Not many owners' manuals recommend nor even make any mention of periodic renewal of brake fluid.
Brakes are operated by hydraulic systems and hence require brake fluid. The exceptions are some vintage cars, which use systems operated by rods and linkages. The hydraulic circuit in a car's braking system is a closed type. That means the fluid never gets consumed and the total volume is always constant.
A low brake fluid level warning is usually triggered by worn brake pads. When the pads thin out after prolonged use, more fluid is required in the piston chambers to maintain the pads in contact with the disc.
This will lead to a drop in the level within the brake fluid reservoir. New, thicker pads will push the pistons back into the chamber, forcing fluid to return to the reservoir.
Another cause for a depleting reservoir is a leak.
But even without a leak, hydraulic fluid degrades over time. So it needs to be replaced. The fluid needs to be pumped out and replaced with fresh fluid. Then the system needs to be bled to expel air bubbles.
It is best to have this done at a workshop at roughly once every 60,000km.