125000785 - 5040DB CHECK ON OPERATION OF WINDSCREEN MISTING SENSOR (Fogging sensor)

With the Examiner set to voltmeter function, select 20 volts end of scale and 5 seconds.Connect the black probe to the vehicle earth and the red probe to pin 3 of the mist sensor output signal.Turn the ignition 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 range.Within this range the sensor supplies a PWM signal proportional to the demisting situation at the windscreen.PWM = 10%

Indicates internal sensor fault This fault is defined as follows:

• Sensor self-diagnostics revealed an internal electrical fault

PWM = 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 faulty or directly radiated by sun70% - Misting intensity from max to moderate60% - Misting intensity from moderate to slight50% - Misting intensity from light to perceptible40% - Misting intensity slightly visible30% - Misting intensity not visible to the human eye20% - Windscreen clean - No misting10% - Internal sensor fault0% - Sensor off or fault in communication or short circuit to GND.