1. Brake System Issues:
* Low brake fluid: This is the most common cause. The brake fluid level sensor detects low fluid, triggering the light. Low fluid indicates a leak somewhere in the system (hose, caliper, master cylinder) which needs immediate attention.
* Faulty brake light switch: This switch is activated when you depress the brake pedal. If it's malfunctioning (worn out, broken, or misaligned), the light will stay on even when the brake isn't applied.
* Worn brake pads: While typically accompanied by other warning signs (noise, vibration), severely worn pads can sometimes indirectly affect the brake system pressure and trigger the light.
* Faulty brake caliper: A sticking or seized caliper can restrict brake fluid flow, also triggering the warning light.
* Leaking wheel cylinder (rear drum brakes): Similar to a caliper issue, a leak prevents proper pressure build-up.
* Master cylinder failure: A failing master cylinder is a serious issue; it's the heart of your braking system. A malfunctioning master cylinder might not always immediately cause a complete loss of brakes, but the light will be on.
* Parking brake engaged: Though less likely to keep the light *constantly* on, a partially engaged parking brake can cause the light to remain illuminated.
2. Electrical Issues:
* Blown brake light bulb(s): Ironically, a burned-out brake light bulb can sometimes trigger the brake light warning. The system might interpret the absence of a bulb as a malfunction. Check all bulbs (including the center high-mounted stop lamp, CHMSL or third brake light).
* Faulty wiring: Damaged, corroded, or loose wiring in the brake light circuit can cause intermittent or constant illumination of the brake light.
* Faulty brake light fuse: A blown fuse in the brake light circuit will prevent the lights from working and may trigger the warning light.
* Faulty instrument cluster: Less common, but a problem with the instrument cluster itself could lead to a falsely illuminated brake light.
Troubleshooting Steps:
1. Check the brake fluid level: This is the first thing to do. If low, locate and fix the leak immediately. Do *not* simply top off the fluid.
2. Check all brake lights: Ensure all bulbs are functioning correctly.
3. Inspect brake pads: Check the thickness of your brake pads.
4. Check the brake light switch: This usually requires some mechanical knowledge and might involve testing the switch with a multimeter.
5. Check fuses: Consult your owner's manual to locate the brake light fuse and check its integrity.
6. Examine the wiring: Look for any obvious signs of damage to the brake light wiring harness.
7. Have a professional diagnose the problem: If you can't pinpoint the cause, it's best to take your Blazer to a qualified mechanic for a proper diagnosis.
Ignoring a brake light can be extremely dangerous. Do not drive your vehicle until the problem is resolved.
