Brake fluid level switch

A low brake fluid level is picked up (in the expansion tank via a reed contact) and notified to the DSC control unit. If the brake fluid level is too low, the DSC is deactivated. Otherwise, there is a danger that air will be drawn into the brake system.

Fig 1: Identifying Brake Fluid Expansion Tank And Brake Fluid Switch

Courtesy of BMW OF NORTH AMERICA, INC.

The brake fluid level switch detects low fluid levels in the brake fluid reservoir. The DSC control unit sends the signal of the bus system to the instrument panel. The instrument panel issues a Check Control message. The usual motion of the brake fluid within the reservoir does not generally trigger a Check Control message. There is a reed contact inserted in the side of the brake fluid expansion tank. The reed contact transmits an electrical signal if the brake fluid level falls below a specified minimum level. The reed contact is closed while the brake fluid level is above the minimum mark.