Volvo S40 Owner's Manual page 140

Limitations
In some situations the BLIS indicator lamp
may illuminate despite there being no other
vehicle within the blind spot.
NOTE
If the BLIS indicator lamp illuminates on iso-
lated occasions despite there being no
other vehicle within the blind spot then this
does not mean that a fault has arisen in the
system.
In the event of a fault in the BLIS system the
display shows the text BLIS Serv.
required .
Here are several examples of situations
where the BLIS indicator lamp may illuminate
even if there is no other vehicle within the
blind spot.
Reflection from shiny wet road surface.
Own shadow on large, light, smooth surface,
e.g. noise barrier or concrete road surface.
Low sun in the camera.
06 Starting and driving
BLIS – Blind Spot Information System (option)
06
139