If your vehicle is showing parking brake does not hold the car on an incline, here are the most likely causes and the parts you'll need to fix each one.
Over time, the steel cables that engage the parking brake stretch from normal use and require tension adjustment to hold the vehicle properly.
The friction material on the parking brake shoes (inside the rear rotor) or the rear brake pads has worn down too far to grip effectively.
If the rear brakes were recently replaced but the internal star wheel adjuster or cable tension wasn't properly calibrated, the brake won't engage fully.
Moisture and road debris can cause the parking brake cable to rust and bind inside its protective sleeve, preventing it from applying full force to the brakes.
On vehicles where the parking brake is integrated into the rear brake caliper, the internal ratcheting mechanism can seize up and fail to squeeze the pads against the rotor.
In severe cases of rust or wear, the parking brake cable can snap entirely, resulting in zero holding power and a completely loose-feeling lever or pedal.