Discovery 2. Manual — part 768

DRIVING AIDS

DESCRIPTION AND OPERATION

86-8-9

Sounder

The PDC sounder is controlled by the PDC ECU and emits a series of tones of varying frequency to inform the driver
of the distance between the vehicle and a detected object.

The PDC sounder is located in the LH side of the luggage compartment. A bracket is attached to the 'E' post, behind
the trim panel and provides for the attachment of the PDC sounder and the PDC ECU.

On vehicles without rear air conditioning, the bracket is located inboard on the LH 'E' post, adjacent to the luggage
compartment trim panel. On vehicles with rear air conditioning, the bracket is located outboard on the LH 'E' post,
adjacent to the outer body panel.

The sounder is located on two screws and lock washers through the bracket and secured with nuts. The sounder is
connected to the PDC ECU via a harness connector.

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86-8-10 DESCRIPTION AND OPERATION

Operation

PDC System Operation
When the ignition switch is in position II and reverse gear is selected, the PDC sensors are automatically activated.
The PDC ECU only activates the system if reverse is selected for more than 1 second. This avoids nuisance audible
warnings when the gear selector lever is being moved between Drive and Park on vehicles with automatic
transmission.

When the system is activated, the PDC ECU illuminates the indicator LED in the PDC switch, switches on the
ultrasonic sensors and generates a single chime on the PDC sounder to indicate the system is active. If an object is
range of the sensors when the system is activated, a series of audible warnings are emitted by the PDC sounder
immediately.

If PDC operation is not required, it can be suspended temporarily by pressing the PDC switch. When reverse is
deselected and subsequently reselected, PDC will automatically become active again.

PDC can also be manually selected when not in reverse gear by pressing the PDC switch. A second press of the
switch is required to turn off the PDC or the PDC will be deactivated if reverse is selected and then deselected.

Sensor Operation
The PDC ECU processes the distance readings from the ultrasonic sensors to determine if there are any objects
within the detection areas. If there are no objects in the detection areas, there are no further audible warnings. If an
object is detected, repeated audible warnings are produced on the PDC sounder.

The maximum detection range is 1800 mm (70 in). When an object is detected, the time delay between the audible
warning tones decreases as the distance between the detected object and the vehicle decreases until, at
approximately 450 mm (17 in), the audible warning tone is continuous.

After the initial detection of an object, if there is no decrease in the distance between an object and the central sensors,
the time delay between the audible warnings remains constant. If an object is detected by one of the corner sensors
only, the audible warnings stop after about 5 seconds if there is no change in the distance between the object and the
corner sensor.

DRIVING AIDS

DESCRIPTION AND OPERATION 86-8-11

Park Distance Control Detection Areas

a Intermittent Warning Tone

b Continuous Warning Tone

Detection Calculation
When operating in the combined transmitter and receiver mode, the sensor outputs a number ultrasonic pulses and
receives the reflected echo signal. The ECU amplifies the received echo signals and compares them with a
preprogrammed threshold to calculate the distance to the object. This is achieved by determining the elapsed time
between the transmission and reception of the ultrasonic signal.

When operating in receiver mode, the sensor receives echo signals transmitted by an adjacent sensor. This mode is
used to improve the accuracy of the system.

The detection cycle consists of the ECU operating one sensor in the combined transmitter and receiver mode and
transmitting a number of ultrasonic pulses. The ECU then switches the transmitting sensor and the adjacent sensor(s)
to receiver mode. After a short time delay, this sequence is repeated using a different sensor to transmit the ultrasonic
pulse and continues until all four sensors have output an ultrasonic signal. This sequence is completed in 100ms. The
ECU uses several measurements of the same sensors to remove errors from the calculation.

If the object is directly behind a sensor, the distance is calculated using the time between the transmission and
reception of the signal. If the object is positioned between two sensors, the ECU uses both signals to determine the
correct distance using triangulation.

To perform the triangulation calculation, the ECU must know the distance between the individual sensors in the
bumper. This information is stored in the ECU memory. From the received distance from each sensor and using the
known distance between adjacent sensors, the ECU can calculate the minimum distance from the vehicle to the
object.

When approaching several objects, the ECU recognises the distance from the vehicle to the nearest object.

A

Y-Y

1800mm (70in)

450mm (17in)

600mm (23.5in)

Y

Y

B

M86 5917

DRIVING AIDS

86-8-12 DESCRIPTION AND OPERATION