1. Hydraulic System Problems:
* Low brake fluid: This is the most common and simplest cause. Check your brake fluid reservoir. Low fluid indicates a leak somewhere in the system (wheel cylinder, caliper, hose, etc.) which needs immediate attention.
* Leaking wheel cylinders or calipers: These components push the brake pads against the rotors. Leaks prevent them from properly retracting, leading to dragging brakes and potentially lockup. You'll see brake fluid leaks around these components.
* Master cylinder failure: The master cylinder is the heart of the hydraulic system. Internal failure can cause inconsistent brake pressure or complete loss of brakes, including lockup.
* Proportioning valve problems: This valve regulates brake pressure between the front and rear wheels. A malfunction can cause uneven braking and potential lockup, especially in the rear.
* Restricted brake lines or hoses: Clogged or severely corroded lines restrict fluid flow, leading to uneven braking and potential lockup.
2. Mechanical Problems:
* Seized caliper pistons: If a caliper piston seizes, it won't retract properly, keeping the brake pad constantly pressed against the rotor. This is a common cause of a single wheel locking up.
* Worn or damaged brake pads: While excessively worn pads don't directly *cause* lockup, they can contribute if combined with other issues like a seized caliper or low brake fluid, as the worn pads might allow more travel before engagement.
* Parking brake cable issues: A stuck or improperly adjusted parking brake cable can keep the rear brakes partially engaged, leading to lockup, especially at low speeds.
* ABS issues (if equipped): Though less likely to cause complete lockup than other problems, a malfunctioning Anti-lock Braking System (ABS) can interfere with normal braking and contribute to uneven pressure. ABS problems usually manifest as a pulsing pedal and/or an illuminated ABS warning light.
3. Other Potential Causes:
* Over-application of brakes: Simply braking too hard can lock the wheels, even with a perfectly functioning system. This is more likely at lower speeds.
Troubleshooting Steps:
1. Check brake fluid level: This is the first thing to do. Low fluid is a serious issue requiring immediate attention.
2. Inspect brake lines and hoses: Look for leaks, bulges, or corrosion.
3. Check for leaks around wheel cylinders and calipers: Look for brake fluid stains or puddles.
4. Inspect brake pads and rotors: Check for excessive wear or damage.
5. Test the parking brake: Make sure it's fully released.
6. Check for ABS warning lights: If the ABS light is on, there's an issue with the ABS system.
Important Note: Brake problems can be extremely dangerous. If you experience brake lockup, get the car inspected by a qualified mechanic *immediately*. Driving with faulty brakes is incredibly risky. Don't attempt repairs yourself unless you have extensive experience working on brakes.
