2002 LAND ROVER DISCOVERY ECU

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86-8-4 DESCRIPTION AND OPERATION
Description
General
Park Distance Control (PDC) is introduced on vehicles from 03 model year. PDC provides an audible warning to the
driver when any obstacles are in the path of the vehicle during a reversing manoeuvre. The purpose of the system is
to assist the driver when parking and is not designed as a crash avoidance system or a replacement for visual
interpretation by the driver.
The system comprises four ultrasonic sensors in the rear bumper, an ECU, a fascia mounted momentary switch and
a sounder unit. The system operates using ultrasonic signals which are transmitted by the sensors. The reflected echo
from this output is received by the sensors and used by the PDC ECU to calculate the distance from an object.
The fascia mounted switch allows the driver to de-activate the PDC system if operation is not required or the vehicle
has a trailer attached.
PDC ECU
A = Vehicles without rear air conditioning
B = Vehicles with rear air conditioning
1Body 'E' post
2PDC ECU
3PDC sounder
4Mounting bracket
The PDC ECU 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 ECU and the PDC sounder.

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DESCRIPTION AND OPERATION 86-8-5
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 bracket has integral studs which provide for the attachment of the ECU with nuts. The ECU is located with the
harness connectors uppermost to assist access. The PDC sounder is located on the opposite side of the bracket and
is secured with screws, lockwashers and nuts.
PDC ECU Connector Pin Details
aConnector C0958
bConnector C0957
Connector C0958
Pin No. Description Input/Output
1 Ignition switch power supply Input
2 Sounder - Negative Input
3 Not used–
4 PDC Switch Input
5 Not used–
6 Reverse Gear signal Input
7 Not used–
8 Ground–
9 Not used–
10 Sounder - Positive 12V supply Output
11 Not used–
12 Not used–
13 PDC Switch LED Output
14 to 16 Not used–

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86-8-6 DESCRIPTION AND OPERATION
Connector C0957
Inputs and Outputs
Two connectors provide the interface between the PDC ECU and the external PDC components.
The ECU receives inputs from the following:
lReverse lamp circuit – for system activation when reverse gear is selected
lPDC switch – for activation and de-activation of the system
lIgnition switch – power supply for system operation.
The ECU outputs to the following:
lSensors – power and ground connections
lSensor – digital signal transmit and receive signals
lSounder – signal for sounder operation
lPDC Switch – power supply for switch LED operation.
Diagnostics
The PDC ECU has no diagnostic connection to enable faults to be retrieved using TestBook/T4. An on-board
diagnostic routine monitors the system and alerts the driver to a system fault by emitting a tone from the sounder.
If a PDC system fault has occurred, the sounder will emit a continuous tone for 3 seconds and the PDC switch LED
will flash continuously when reverse gear is selected.
Pin No. Description Input/Output
1 Not used–
2 Sensor - RH Inner - Signal Input
3 Sensor - Rear LH Inner - Signal Input
4 Sensor - Rear RH Outer - Signal Input
5 Sensor - Rear LH Outer - Signal Input
6 and 7 Not used–
8 Ground - All sensors Input
9 Not used–
10 Power Supply - All sensors Output
11 and 12 Not used–

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DESCRIPTION AND OPERATION 86-8-7
Sensors
Four sensors are positioned in the rear bumper. Each sensor comprises an outer housing with an angled rubber trim
which differs between the inner and outer sensors and the sensor body. The outer housing has a slot which engages
with a pin on the sensor body and is locked by rotating the sensor. A coil spring around the sensor is compressed
when the sensor is installed in the bumper and maintains the sensor housing engaged on the pin. The sensor housing
has a raised lip at the top which locates in a corresponding groove in the bumper mounting hole and sets the correct
orientation for the sensor body.
Each sensor has a three pin connector which connects into a common harness linking all four sensors. This harness
is connected to the main vehicle body harness. The three pins are for sensor negative and positive feeds and a signal
line.
Each sensor comprises a plastic housing which contains a piezoelectric disc. The disc resonates at a frequency of
38.4kHz, producing an ultrasonic signal output. The disc also receives the reflected echo signal.
The PDC ECU controls the operating mode of each sensor by output of a digital signal on the signal line. Each sensor
has two modes of operation; combined transmitter and receiver mode or receiver mode only.

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86-8-8 DESCRIPTION AND OPERATION
PDC Switch
The PDC switch is located in the instrument pack cowl, below the fuel flap release switch. The switch has a
momentary, non-latching action, which switches a positive output from the PDC ECU to ground when pressed. This
signal is used by the ECU to switch the PDC between the activated and de-activated conditions. The switch is
connected to the PDC ECU via a harness connector which is integrated into the vehicle body harness.
The switch contains an LED. The LED illuminates for approximately 3 seconds when the ignition is switched to
position II for a bulb check. The bulb check is controlled by logic within the PDC ECU. When the system is active (i.e.
obstacle detected), the LED illuminates to show the active condition.
When the PDC is switched from the off condition to the active condition, the LED is illuminated briefly, along with a
chime from the sounder, to signal that the system has been activated.
If a fault exists in the PDC system, the ECU flashes the LED continuously, when the switch is pressed to activate the
system.

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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.

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DESCRIPTION AND OPERATION 86-8-11
Park Distance Control Detection Areas
aIntermittent Warning Tone
bContinuous 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)
YY
B
M86 5917