Brake Fluid Level Warning Switch

WARNING: This page is about a different car, the 2003 Lexus RX 300 and 2002 Lexus RX 300. However, it is still accessible from the selected car via links, so may be relevant.

Remove the reservoir tank cap and strainer and disconnect the connector.
Check that no continuity exists between the terminals with the switch OFF (float up). See Fig 1.
Use siphon, etc. to take fluid out of the reservoir tank.
Check that continuity exists between the terminals with the switch ON (float down).
Pour the fluid back in the reservoir. If operation is not as specified, replace the switch.

Fig 1: Inspecting Brake Fluid Level Warning Switch Continuity