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Exterior Fitting
5. Receiver diodes (100% light received)
6. Water droplets/film
7. Receiver diodes (less than 100% light received)
8. Lost light
A. Clean, dry windscreen
B. Wet and dirty windscreen
The sensor contains transmitter and receiver diodes which
transmit and receive infrared light which is directed onto the
windscreen via an optical unit. The light is directed at an angle
so that the light is reflected 100% on the outside surface of the
screen and is transmitted back into the optical unit. To receive
a 100% reflection the screen outer surface must be clean and
dry.
The light is reflected four times from when it leaves the
transmitter diodes to when it is picked up by the receiver
diodes. If the windscreen is wet or dirty in the area of the
optical unit, the clean conditions required for 100% reflection
means that some of the light reflected is lost. As the screen
becomes dirtier or wetter, the received light is evaluated
by the rain sensor and translated into a signal value.
micro-controller within the rain sensor monitors the change
in signal and initiates the appropriate wipe cycle via LIN Bus
signals to the BCM.
The software can compensate for the long term effects
scratches and stone chips in the area of the optical unit and
short term effects of dirt or smears caused by worn wiper
blades. A heater element is also contained within the rain
sensor and uses ambient temperature signals from the BCM
to keep the optical unit clear of frost or condensation.
The sensitivity of the rain sensor can be adjusted by the driver
using the intermittent rotary switch on the wiper lever. The
period between wipe cycles can be increased or reduced
manually by the driver to suit prevailing conditions. In very
heavy rain the sensor will operate the wipers continually.
When several continuous wipe cycles have taken place,
the sensor will maintain the continuous operation to avoid
Version 2.0
switching back to intermittent from a continuous wipe and
back again.
The rain sensor receives vehicle speed information from
the ABS ECU via the BCM every two seconds. The sensor
increases the sensitivity as the speed increases to optimise the
wiper operation. When the vehicle speed is reduced to less
than 8 km/h, the sensitivity is automatically reduced. Below
this speed the wipers will only operate continuously in very
heavy rain.
A light sensor is incorporated into the sensor and is used to
increase the sensitivity of the sensor when light levels are low.
This feature counteracts the effects of rain on the windscreen
affecting the driver's vision during night time driving.
Diagnostics
A diagnostic socket allows the exchange of information
between the BCM, rain sensor and diagnostics tool. The
diagnostic socket is located in the driver's footwell and is
constructed to the ISO 15765 standard. A socket connects
directly to the CAN Bus and allows the retrieval of diagnostic
information and programming of certain functions to be
A
performed. The BCM forms the gateway for the CAN Bus
link to other electronic control units. The BCM also translates
diagnostic messages from diagnostics tool into CAN Bus
messages recognised by the system components.
The rain sensor can store fault codes which can be used to
diagnose faults or non function of the rain sensor. The faults
are stored in a non-volatile memory which retains the logged
fault codes even when the supply is disconnected. If a rain
sensor fault prevents the sensor from operating, the BCM will
control the wiper system as if a rain sensor is not fitted.
The BCM monitors all inputs and outputs related to the
wiper system and other BCM controlled functions. If a fault
is detected a code applicable to that fault is stored in a fault
log. Two fault logs are provided within the BCM for internal
and external faults. The BCM is capable of detecting open and
short circuits and also incorrect LIN Bus messages.
Wipers and Washer
734
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