Volvo 2007 S80 Owner's Manual page 143

NOTE
The red warning light may be difficult to see in strong sunlight or when sunglasses are being worn.
WARNING
Cruise control only warns of vehicles detected by the radar sensor, see
warning or the warning may be delayed. The driver should always apply the brakes when necessary.
Automatic deactivation
Adaptive cruise control is linked to other systems such as the stability and traction control system (DSTC). If any of
these systems are not functioning properly, adaptive cruise control is automatically deactivated.
In the event of automatic deactivation a signal will sound and the message
display. The
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04 Comfort and driving pleasure
Adaptive Cruise Control-ACC
driver must then intervene and adapt the vehicle's speed to the surrounding traffic. Automatic deactivation may be
caused if:
the vehicle's speed falls below 20 mph (30 km/h)
the wheels lose traction or if the anti-lock brake system is activated
brake temperature is high
engine speed (rpm) is too low
the radar sensor is obstructed by, for example, wet snow or rain.
The radar sensor and its limitations
The radar sensor is used both by the adaptive cruise control and the collision warning system. It is designed to detect
vehicles or larger vehicles driving in the same direction as your vehicle. The radar sensor does not detect pedestrians,
or oncoming, slow or stationary vehicles and objects. Warnings are not given and the brakes are not applied in such
cases.
WARNING
Accessories or other objects must not be installed in front of the grille.
Modification of the radar sensor could make its use illegal.
The radar sensor's capacity to detect vehicles ahead is impeded:
if the radar sensor is obstructed and cannot detect other vehicles, for example in heavy rain, or if snow or other
objects are obscuring the radar sensor.
NOTE
Keep the area in front of the radar sensor clean.
page 146. In some cases there may be no
Cruise Control Canceled is shown in the