2004 Cadillac Deville Brake Fluid Light

The sensor attaches to the reservoir. Try disconnecting it and see if your message goes away. If it don't short the terminals together with a paper clip, wire, or something, and see if it goes off then. If one method or the other makes it go away, and you have to replace the sensor, here is the procedure:

Brake Fluid Level Indicator Switch Replacement
Caution: Refer to Brake Fluid Irritant Caution in the Preface section.

Notice: Refer to Brake Fluid Effects on Paint and Electrical Components Notice in the Preface section.

Removal Procedure

Disconnect the electrical connector (1) from the brake fluid level sensor.

Using a needle nose pliers carefully depress the retaining tabs (1) on the end of the brake fluid level sensor and press the sensor through the reservoir to remove.
Installation Procedure

Align the brake fluid level sensor to the master cylinder reservoir.
Press the brake fluid level sensor into the master cylinder reservoir.
Connect the electrical connector to the brake fluid level sensor.