2429806 - 5040DB Check on operation of windscreen misting sensor

With the Examiner on the voltmeter function, select full scale deflection of 20 volts and time base of 5 seconds. Connect the black probe to the vehicle earth and the red probe to pin 3 of the fog sensor. Turn the key on and press the START button. The signal displayed must be a PWM pulse train with a frequency of 100 hz and a Duty Cycle that varies between 10% and 90% as shown in the attached table.

The first 100 sensor output readings must not be considered (1 sec).

Pin out:

• 1. earth
• 2. +15
• 3. not connected
• 4. signal output

PWM% Duty Cycle = T1 / T2 where:

• T1 = pulse duration
• T2 = 1/f = 1/100 Hz = Transmission duration
• T2 = 10msec ± 7%

PWM from 20% to 70%This is the normal sensor operating rangeWithin this range, the sensor will supply a PWM signal proportional to the amount of misting on the windscreen.PWM = 10%Indicates internal sensor fault This fault is defined as follows:sensor self-diagnostics revealed an internal electrical faultPWM = 80%This condition indicates a sensor limit condition. This is defined as follows:The sensor optics are saturated due to excessive direct sunlight.The signal is transmitted as long as the above limit condition persists.PWM = 90%This condition indicates a limit condition or sensor fault. This is defined as one of the following:Sensor optics are saturated due to excessive reflected energy. This may be due to a very high level of misting or an object between the windscreen surface and sensor.Sensor internal temperature reached and exceeded 70°C. The internal process is disabled to avoid damage. A fault signal is transmitted as long as the excess temperature persists.PWM = 0 % and 100%These two statuses will never be transmitted by the sensor.Certain hardware faults may be interpreted by the receiving input stage as PWM signals of 0% or 100%. This is due to the static nature of the signal (microcomputer not processing or under conditions of s.c. to +12V or GND or open circuits).Messages transmitted by PWM100% Sensor off or fault in communication or s.c. to +12V90% Sensor saturated or blocked or with excess temperature80% Sensor fualty or directly radiated by sun70% Misting intensity from Max. to moderate60% Misting intensity from moderate to light50% Misting intensity from light to identifiable40% Misting intensity slightly visible30% Misting intensity not visible to the human eye20% Windscreen clear - No misting10% Internal sensor fault0% Sensor off or fault in communication or s.c to GND.