Brake fluid level switch

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

Fig 1: Identifying Brake Fluid Level Switch

Courtesy of BMW OF NORTH AMERICA, INC.

Index	Explanation
1	Sealing cap with brake fluid level switch
2	Brake fluid expansion tank
3	two-pin plug connection

The brake fluid level switch is activated in response to a low fluid level 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 permanent magnet in the moving float; this triggers the reed contact in the brake fluid level switch firmly fitted in the fuel tank. Here, the reed contact converts the float movement into an electrical signal. The reed contact is closed while the brake fluid level is above the minimum mark.