* Anti-lock Braking System (ABS) malfunction: A problem with the ABS system itself is a common cause of brake lockup *or* the *inability* to lock the brakes (which is the ABS's *intended* function). A faulty ABS sensor, control module, or hydraulic component can lead to unpredictable brake behavior, including lockup.
* Brake System Leaks: A leak in the brake lines, wheel cylinders, or calipers will cause a loss of brake pressure, potentially leading to a locked-up brake if pressure is unevenly distributed across the wheels.
* Seized Calipers or Wheel Cylinders: These components can seize up, preventing the brake pistons from retracting properly, leading to constant braking force on one or more wheels.
* Low Brake Fluid: Extremely low brake fluid levels indicate a serious problem, likely a leak somewhere in the system, resulting in inconsistent or failing braking power and potential lockup.
* Overly Tight Parking Brake: While this is usually obvious, an improperly adjusted or malfunctioning parking brake can contribute to wheel lockup if it is not completely released.
* Improper Brake Adjustment: If the brakes aren't adjusted correctly, it could cause uneven brake pressure and potentially lead to lockup.
To find the specific cause, you'll need a proper diagnosis. This could involve:
* Visual inspection: Check brake lines for leaks, and calipers and wheel cylinders for signs of seizing.
* Brake fluid level check: Ensure the fluid level is within the normal range.
* ABS diagnostic test: Use an OBD-II scanner capable of reading ABS codes. A mechanic can do this.
* Brake pressure test: A mechanic can perform this test to check for pressure inconsistencies within the brake system.
Driving with locked brakes is extremely dangerous. If you're experiencing this issue, do *not* continue to drive the vehicle. Have it towed to a qualified mechanic for repair.
