If it flashes longer or lights up while driving, you should stop immediately and check the brake fluid level. It is possible that one of the brake circuits has lost its tightness and as a result it has failed, which you additionally feel by the extended pedal travel (brake pedal adjustment and information on this topic in the chapter Brakes).
Tips: Low brake fluid level may be due to badly worn brake pads. Reason: as the brake pistons wear out, they extend further out of the cylinders and make room for brake fluid, the level of which, if you follow the logic, in the reservoir decreases.
If the brake fluid level indicator light comes on, you should measure the thickness of the pads unless you find another defect. In this case, do not add brake fluid to the reservoir, but replace the pads. To do this, you need to press the pistons in the brake calipers. Consequence: the brake fluid level will rise again to the nominal value. The mistakenly poured brake fluid will spill out of the reservoir.
Troubleshooting
1. Checking the indicator light.
2. If the control lamp lights up when the engine is running, although the fluid level in the expansion tank is above the "MIN" mark, for the sake of experiment, disconnect the connector on the expansion tank fluid level sensor.
3. If the light goes out, the sensor in the expansion tank is faulty – replace the tank.