GF54.30-P-4001T Coolant/Washer Fluid Level Voltage Coding, Function

GF54.30-P-4001T Coolant/washer Fluid Level Voltage Coding, Function

Component Identification:

The coolant level indicator switch (S41) and the windshield washer fluid level indicator switch (S42) are connected in series and are read in by the driver-side SAM control unit with fuse and relay module (N10/1).

Voltage coding
Voltage coding is used in order to allow several switches to be interrogated over 2 lines. Each switch is connected in parallel with an internal resistor. The resistors (r1 and r2) of the series-connected switches (s1 and s2) have different resistances. These resistors (r1 and r2) form, with open switches (s1 and s2) together with the resistor (r3) of the driver-side SAM control unit with fuse and relay module (N10/1) a voltage divider which is supplied with the constant voltage (u). Via the voltage (u e) the driver-side SAM control unit with fuse and relay module (N10/1) can distinguish between 6 different states. As shown above, the line which leads from the resistor (r3) to the driver-side SAM control unit with fuse and relay module (N10/1) serves as a reference line.

The reference line is used to determine the voltage difference between the direct line and the line running via the switches (s1 and s2) or the resistors (r1 and r2). The two fundamental states are open circuit and short circuit. The 3rd state describes the case where both fluid levels are above the minimum mark and therefore both switches (s1 and s2) are open and the current is flowing through both resistors The 4th state describes the case where both fluid levels are below the minimum mark and therefore both switches (s1 and s2) are closed and the current is not flowing through both resistors (r1 and r2). The 5th and 6th states describe the case where one of the two fluid levels is below and the other is above the minimum mark. By means of the input voltage the driver-side SAM control unit with fuse and relay module (N10/1) detects whether the current flows through the resistor (r1) or the resistor (r2).

Switch status and messages
Using the coolant level indicator switch (S41) and the windshield washer fluid level indicator switch (S42) a total of the following switch combination alternatives result and the consequent displays on the multifunction display (A1p13):
^ When the coolant level indicator switch (S41) is open and the windshield washer fluid level indicator switch (S42) is open, no message appears on the multifunction display (A1p13).
^ When the coolant level indicator switch (S41) is open and the windshield washer fluid level indicator switch (S42) is closed, the message "ADD WINDSHIELD WASHER FLUID" appears on the multifunction display (A1p13).
^ When the coolant level indicator switch (S41) is closed and the windshield washer fluid level indicator switch (S42) is open, the message "CHECK COOLANT LEVEL" appears on the multifunction display (A1p13).
^ When the coolant level indicator switch (S41) is closed and the windshield washer fluid level indicator switch (S42) is closed, the message "CHECK COOLANT LEVEL" and the message "ADD WINDSHIELD WASHER FLUID" appear alternatively on the multifunction display (A1p13).

Evaluation
The voltage (u e) is applied at the input of the analog-digital-converter (ADC) of the driver-side SAM control unit with fuse and relay module (N10/1). The ADC converts the analog voltage into a digital value. The processor compares the digitized value with the threshold values stored in memory and if necessary, passes the appropriate messages "Check coolant level" and "Please refill washer fluid" on the class B (interior) controller area network bus (CAN-B). The instrument cluster (A1) reads in these messages from the CAN B and actuates the multifunction display (A1p13) accordingly.

Acknowledgment of messages (up to 31.5.05)
Warning and error messages can be acknowledged automatically or manually. Manual acknowledgment takes place by pressing the steering wheel buttons, scroll forward/back button (S110s1) and System selection button (S110s3) or the instrument illumination brightness control and reset button (A1r1). If the cause of a message which can be acknowledged is not applicable, the warning is displayed in the multifunction display (A1p13) for the duration of its minimum display time.

Acknowledgment of messages (as of 1.6.05)
The windshield washer fluid level message is displayed as of circuit status "Circuit 15C ON" and is acknowledged automatically after 5 s. Acknowledgment by pressing the steering wheel buttons scroll forward/back button (S110s1) and system selection button (S110s3) or instrument illumination brightness control and reset button (A1r1) continues to be possible.