Vauxhall ASTRA Owner's Manual page 218

Flashing:
The fault is due to sensors obstructed with
snow or ice. The sensors must be
undamaged and free of dirt, snow and ice.
Interference due to external sources of
ultra sound (e.g. pneumatic drills, rotary
machines). Once the source of interference
is removed, the system will operate
normally.
Caravan/trailer towing equipment 3,
caravan/trailer towing
The system automatically detects if a
towbar is properly fitted to the vehicle.
When towing, plugging the trailer cable
into the socket automatically switches the
parking distance sensor off
Fitting rear load racks 3
Rear load racks, e.g. bicycle racks, fitted
near the sensors could disrupt the system.
Observe the note on the Astra TwinTop on
page 58.
Driving and operation
Automatic level control 3
Automatic level control makes it possible to
keep the height of the vehicle constant
when subjected to different loads in the
rear (e.g. when towing a caravan or trailer).
This significantly improves driving
conditions.
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