Land Rover Discovery Owners & Service Manuals

Land Rover Discovery: Detection Calculation

In the combined mode, the sensors emit a series of ultrasonic impulses and then switch to receiver mode to receive the echo reflected by an obstacle within the detection range. The received echo signals are amplified and converted from an analogue signal to a digital signal by the sensor. The digital signal is passed to the Parking Aid Control Module (PACM) and compared with pre-programmed data stored in an Electrically Erasable Programmable Read Only Memory (EEPROM) within the PACM. The PACM receives this data via the signal line from the sensor and calculates the distance from the object using the elapsed time between the transmitted and received impulse. The duration of the impulse duration is determined by the module, with the sensor controlling the frequency of the impulse output.

When in Reverse (R) gear, both the front and rear sensors are active, when in a forward gear, only the front sensors are active.

In receiver mode, the sensor receives impulses that were emitted by adjacent sensors. The PACM uses this information to precisely determine the position and distance of the object.

If no objects are detected there are no further warning tones. If an object is detected, repeated audible tones are emitted from either the front or rear audio speakers as appropriate. The time delay between the tones decreases as the distance between the object and the vehicle decreases, until at approximately 300 mm (12 inches), the audible tone becomes 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 approximately 3 seconds if there is no change in the distance between an object and the corner sensor.

When approaching several objects within detection range, the PACM recognizes the distance from the vehicle to the nearest object.

The Parking Aid Control Module (PACM) will prioritize the objects detected, the nearest object detected will take priority and the corresponding audio outputs will be emitted. For example if 2 objects are detected (one front one rear) the nearest detected object will take priority and relevant audible tone will be heard.

If two objects are detected at equal distance (one front one rear) the audible tones will alternate between the front and rear audio speakers.

The volume output of the parking aid audible tones can be adjusted using the audio volume control when the parking aid system is activated. The volume can also be adjusted from the home menu screen by selecting 'Setup', 'System' followed by 'Volume Presets' on the Audio Head Unit (AHU) or Touch Screen (TS). The volume can be adjusted using the + or - selections on the AHU or TS.

The PACM receives a signal on the High Speed (HS) Controller Area Network (CAN) chassis bus from the Central Junction Box (CJB) with contribution of the Gateway Module (GWM), when a trailer is fitted. When this signal is detected, the PACM suspends operation of the rear parking aid system. The ignition needs to be cycled once the trailer has been disconnected to activate the rear parking aid system.


360º Parking aid system automatically becomes active when the parking aid system is turned on via the parking aid switch or if Reverse (R) gear is selected.

The park assist sensors will monitor the vehicles surrounding area. When an object has been detected and then moves out of the sensor's range, it will then be tracked. The software which the Parking Aid Control Module (PACM) implements, takes into consideration the trajectory of the vehicle based on the vehicle speed and steering wheel angle.

The PACM will then inform the driver via the Touch Screen (TS) or Audio Head Unit (AHU) (depending on vehicle specification), the information the PACM received from the park assist sensors. The PACM relays information to the TS or AHU, using the High Speed (HS) Controller Area Network (CAN) chassis bus. The TS or AHU will then receive this using the Medium Speed (MS) CAN chassis bus via the Gateway Module (GWM).

The TS or AHU will then display an on screen plan view of the vehicle with predefined zones and sectors around it. The location and distance of an obstacle is represented by bars.

The bars are colour coded:

  • Red - close range and object in collision course.
  • Amber - mid range and object in collision course.
  • Yellow - far range and object in collison course.
  • Grey - any range and object not in collision course.

The 360º parking aid system also provides a warning audio alert. On a threat of detection within the predefined range, audio beeps are reproduced. As the distance to threat diminishes the repitition frequency increases. At the minimum safe guard distance the beeps turn into constant tone.

When the directional of which a threat of an object is detected, the warning alert can be heard in the relevant speaker.


When park assist system is switched on. The park assist switch is used to scroll through the three park assist options:

  • Parallel parking.
  • Perpendicular parking.
  • Parking exit.

When selected, instructions for the three park assist options are displayed in the Instrument Cluster (IC) message center.

Instructions are then communicated to the driver using the following methods:

  • Visual - graphical and text message instructions in the Instrument Cluster (IC) message center.
  • Audible - variable sound tones through vehicle speakers.

The park assist system only becomes active when the vehicle speed is less than 30 km/h (18 mph).

The park assist system must not be used if:

A temporary spare wheel is in use.

A sensor is damaged or the bumper is damaged sufficiently to affect a sensor mounting point.

A sensor is obstructed by items attached to the vehicle, e.g, bumper covers, a bicycle rack, a trailer, stickers, etc.

The vehicle is being used to transport a load that extends beyond the vehicle perimeter, for example a trailer.

During any park assist manoeuver, the parking aid system will remain active and will sound when objects are detected near the vehicle. A parking manoeuver can be cancelled at any point by holding/turning the steering wheel or by pressing the park assist button.


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