939010269 - 5040DB Check windscreen demister sensor operation (Automatic Air Conditioning)

Using an Examiner set to the Voltmeter mode, select a 20 Volt full scale deflection and 5 seconds, connect the black probe to the vehicle earth and the red probe on pin 3 of the mist sensor output signal, turn the key on and press the START button.The signal shown should be a set of PWM impulses with a frequency of 100 Hz and a Duty Cycle that varies between 10 and 90% as indicated in the table below.

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

1. earth2. +153. not connected4. signal outputPWM% Duty Cycle = T1 / T2 where:

• T1= duration of impulse
• T2 = 1/f = 1/100 Hz = Duratation of transmission
• T2 = 10msec ± 7%

PWM of 20% at 70%This is the normal sensor operating range.Within this range, the sensor supplies a PWM signal proportional to the amount of condensation present on the windscreen.PWM = 10%Indicates an internal sensor fault. This fault is defined as follows:the sensor self-diagnosis detected an internal electrical problem.PWM = 80%This condition indicates a sensor limit condition. This is defined as follows:The sensor optics are saturated due to too much direct sunlight.The signal is transmitted as long as the limit condition described above persists.PWM = 90%This condition indicates a sensor limit condition or failure. It is defined as one of the following:The sensor optics are saturated due to too much reflected energy. This may be due to a very high level of condensation or an object between the windscreen surface and the sensor.The internal sensor temperature reached and exceeded 70°C. The internal processor is disabled to avoid damage. A fault signal is transmitted as long as the excess temperature persists.PWM = 0 % and 100%These two conditions will never be transmitted by the sensor.Specific hardware faults may be interpreted by the receiving input stage as PWM signals or 0% or 100% due to the static nature of the signal (microcomputer that does not process or conditions of dc to +12V or GND or open circuits).Messages transmitted by PWM100% Sensor " off " or fault in communication or d.c. to +12 V90% Sensor saturated or locked in excess temperature80% Sensor faulty or subject to direct sunlight70% Condensation intensity Max to moderate60% Condensation intensity moderate to slight50% Condensation intensity light to identifiable40% Condensation intensity slightly visible30% Condensation intensity not visible to the human eye20% Windscreen clean - No condensation10% Internal sensor fault.0% Sensor " off " or fault in communication or d.c. to GND