Electrical -- Basic Knowledge -- 251 Chassis: Maintenance Mercedes-Benz R-class W251 facelift

Coolant/washer fluid level voltage coding, function - GF54.30-P-4001RT

MODEL 251.1/0 up to Model Year 8

Voltage coding

For voltage coding the switches "s 1 " and "s 2 " are connected in" parallel with the resistances "r 1 " and "r 2 " (the values of "r 1 " and "r 2 " must differ).

When the switches are open, together with "r 3 " of the front SAM control unit (N10), these resistors form a voltage divider which is supplied with the constant voltage "U const ".

The voltage "U e " at the inlet of the front SAM control unit is therefore dependent on the positions of the switches and the values of the resistances.

With the two switches, there are therefore four possible switch combinations (see table).

Each of these combinations results in a different voltage value "U e " at the input of the front SAM control unit.

Evaluation

The voltage "U e " is applied at the input of the Analog-Digital converter of the front SAM control unit. The analog/digital converter converts the analog voltage into a digital value.

This is necessary as the processor of the front SAM control unit can only work with digital values.

The processor compares the incoming values with the threshold values stored in the memory and, as need be, outputs the corresponding message (coolant level and/or washer fluid level too low) over the interior compartment CAN. The instrument cluster (A1) reads this message and actuates the multifunction display (A1p13) for the picture and text accordingly.

With known resistance values and a known voltage "U const", "U e " can be calculated with the following formula: U e = U const (r 1 + r 2 )/(r 1 + r 2 + r 3 ). The following table shows the warning messages which appear according to the status of the switches

These messages can be acknowledged with the trip odometer reset button (A1s3) on the instrument cluster

Reset, function - GF54.50-P-2010RT

MODEL 251.1/0 up to Model Year 8

Reset the long-distance memory ("since reset")

1. "Tml. 15 ON"
2. Using the system selection button (S110s3) and scroll forward/back button (S110s1) of the multifunction steering wheel, select the "as of reset" display screen.
3. Keep the instrument and controls illumination button, dim (A1s5) or Instrument and controls illumination button, bright (A1s4) and trip odometer reset button (A1s3) pressed for one second.
4. The display is reset.

Manual reset of short-distance memory ("since start")

1. "Tml. 15 ON"
2. Using the system selection button and scroll forward/back button of the multifunction steering wheel, select the "since start" display screen (short-distance memory).
3. Keep the instrument and controls illumination button, dim or instrument and controls illumination button, bright and trip odometer reset button pressed for one second.
4. The display is reset.

Automatic reset of short-distance memory ("since start")

As the display "since start" (short-distance memory) is intended for the data of one driving cycle, the contents of the "since start" display (short-distance memory) are reset automatically.

If the EIS [EZS] control unit (N73) is in position "circuit 15C", all the values of the short-distance memory are reset after approx. four hours. If during this time "circuit 15C" is interrupted by "circuit 15R ON" or "circuit 15 ON", the erasure time window (four hours) starts again

Adoption of the data from the previous driving cycles in the short-distance memory

In many cases it may be meaningful to adopt the data from the previous driving cycles in the short-distance memory, because, for example, the data for a tank filling during a vacation trip should also be recorded during any trip interruptions. The data for the entire trip can then be stored in the long-distance memory ("since reset").

The procedure for this is as follows

1. Using the system selection button and scroll forward/back button of the multifunction steering wheel, select the "since start" display screen (short-distance memory).
2. Start the engine.
3. The "since start" (short-distance memory) flashes for up to 2 km or miles or 2 minutes after starting the engine.
4. With a flashing display keep the instrument and controls illumination button, dim or instrument and controls illumination button, bright and trip odometer reset button pressed for one second.
5. The values of the previous driving cycle are incorporated in the short-distance memory.

If the display of trip time or mileage exceeds the maximum display value (40959 miles (65535 km) or 99:59 hours), then the trip time and mileage of the respective memory is reset automatically. This preserves the relationship between trip time and mileage

After a reset it may take as much as 3 km or 2 minutes until the trip computer has enough data to display the fuel consumption figures correctly. The national version of the instrument cluster is displayed depending on the setting (kilometers or miles) and coding A1