The flashing P warning sign on a BMW 320 D means that the parking brake is engaged. This is a safety feature that helps prevent the car from rolling away when it is parked. The parking brake should be engaged when the car is parked on a hill, in a parking garage, or in any other situation where it could roll away.
To engage the parking brake, pull up on the parking brake lever located between the front seats. The parking brake is disengaged by pushing down on the lever.
If the parking brake warning sign is flashing while you are driving, it means that the parking brake is not fully engaged. This can be dangerous because the car could roll away if it is not properly parked. Pull up on the parking brake lever until the warning sign turns off.
If the parking brake warning sign is flashing and the parking brake is fully engaged, it means that there is a problem with the parking brake system. You should take your car to a qualified mechanic to have the parking brake system inspected.