Park Distance Control (PDC) uses sonar sound waves and high-tech electronics to guide you in tight parking situations. PDC helps you park by audibly indicating when you are near an object, typically a parked car.  

Benefits of PDC:

• By warning you of the distance between your car and another object, PDC is an excellent device for protection against accidental damage. 
• PDC makes it easier to maneuver in confined spaces or in conditions with poor visibility.
• PDC can detect living creatures too, so the system helps not only to prevent damage to vehicles, but also to small children, stray animals, etc.

There are 4 ultrasonic sensors in the front bumpers, two in the corners of the rear bumper, and two in the center of the rear bumper.

• The rear corner sensors trigger a beeping tone when an obstacle is within 24 inches.
• The rear center sensors indicate objects at 59 inches.
• All sensors indicate objects are within 12 inches by changing the beep to a solid tone.

The tones emanate from the appropriate part of the car, and the tones become more rapid as the distance narrows. A higher-pitch beep warns of objects near the front of the car, while a lower tone indicates objects near the rear of the car.

The system automatically engages when shifting into reverse and automatically disengages after driving 164 feet or reaching a speed of 18 mph. 

You can turn the system on or off manually with a console switch. 

The principle behind PDC is ultrasonic sonar distance measurement, similar to the sonar systems used in the open sea to detect objects on the ocean floor. 

Sample Schematic Diagram.

1. An electronic source unit generates a signal. 
2. The signal is transmitted, bounces off an object and returns to the source. 
3. Based on the " echo", the amount of time it takes for the signal to return, the sonar takes a picture of nearby objects.

In the new E65 7 Series, PDC has a graphical display with iDrive:

The graphical indicator shows a top-level view of the parking zone. Known obstacles are shown by colored fill-ins of the surfaces inside of the detection area. Using the image display, the driver has an overview of all obstacles within the detection area. The display illustrates obstacles that move towards the vehicle, and the objects become larger as the vehicle approaches them. The driver can therefore see the shape and size of the obstacles and avoid collision within the danger zone. The optical warning activates earlier than the warning sound. The detection area spans 1.5 meters to the front and 2 meters to the rear.

BMW USA interactive page on PDC.

BMW South Africa informative page on PDC.

PDC retrofit accessory is available for recent BMW models. Find out more about the accessory here:

• Peake BMW
• Circle BMW

Eyes in the Back of Your Head article from Edmunds describes ultrasonic sensors using the BMW 7 Series as an example.

Good old parking sonar describes a homemade parking sonar system. Some great tips for automotive electronics projects.

Tip: Try your own search using keywords like "sonar parking" or "parking clearance sonar".