If your vehicle is showing car rolls away or creeps forward while shifted into park, here are the most likely causes and the parts you'll need to fix each one.
The bushing connecting the shift cable to the transmission wears out or breaks. The shifter inside the car moves to Park, but the transmission actually remains in Reverse or Neutral.
Often occurring after recent transmission or engine work, an improperly adjusted shift cable prevents the transmission lever from fully engaging the Park position.
If a 4WD transfer case is accidentally shifted into Neutral or its shift motor fails between gears, the transmission's parking lock is completely disconnected from the wheels.
The transmission's Park setting locks the output shaft. If a drive axle or driveshaft breaks, the mechanical link to the wheels is severed, allowing the vehicle to roll freely.
The internal metal pin that physically locks the transmission gears can snap if the vehicle is forcefully shifted into Park while still rolling at speed.