If a steady red brake light comes on your dash, there could be a number of issues at play. Let’s discuss each of them in terms of priority:
1. Low Fluid
Check the master cylinder reservoir to ensure that the fluid level is above the “low” line. If the level is low, this typically suggests some kind of leak in the brake system. Since brake systems are hydraulically sealed, this condition should not occur. (More about brake fluid here.)
2. Worn Brake Pads
Not all vehicles will indicate pad condition with a dashboard brake light. Either way, you should check your brake pads frequently. If your pads are worn, get them replaced immediately.
3. Worn Wear Sensors
Some auto brands use the dashboard brake light to announce that a wear sensor has gone off.
4. Electrical Fault
If you investigated everything above and nothing appears to be wrong, it is likely a sensor may have gone south. In this case, an on-board diagnostic (OBD) technician can tell you what codes are at work and how to get them re-set or replaced.
In all cases, consult your owner’s manual.