Displaying fuel level, function - GF54.30-P-3018R

MODEL 230

Networking

Fig 1: Displaying Fuel Level - Signal Communication

Courtesy of MERCEDES-BENZ USA

Function requirements

Terminal 15 ON

Function

The fuel level sensor (B4) changes its resistance according to the fuel level in the tank. The fuller the tank, the lower the resistance.
The resistance of the fuel level sensor (B4) is registered by the rear SAM control module (N10/8).
The rear SAM control module (N10/8) converts the resistance values of the fuel level sensor (B4) into a percentage . (A full tank is 100 %.)
The rear SAM control module (N10/8) relays this percentage onto the interior compartment CAN.
The instrument cluster (A1) registers this percentage from the interior compartment CAN and actuates the fuel level and reserve gauge (A1p2), and the fuel reserve warning lamp (A1e4) if necessary.
The fuel level and reserve gauge (A1p2) is driven by a stepper motor.
The needle moves round to the display value within t = 1 s.

Engine start

When the engine starts, a time constant of t = 0.8 s is selected for max. t = 6 s in order to obtain a display reading with the full onboard voltage. After this period of t = 6 s, or as soon as the vehicle starts to move (v > 0), the display reading is computed and displayed via a linear run-on inhibitor (programmable).

Fuel level display

When the EIS control module (N73) is in the terminal 15 ON position, the current fuel level is displayed in the fuel level and reserve gauge (A1p2).

Refueling detection

If the vehicle is refueled with the EIS control module (N73) in the terminal 15 ON position, the refueling is only detected (and the display updated) if at least 7 liters of fuel are added to the tank. The display is updated the next time terminal 15 is switched ON. There is always a delay before the display is updated. This inhibits fluctuations in the display, e.g. due to cornering.

Reserve range

The reserve range extends from "0" to "R". This corresponds to approx. 10 liters of fuel.
When the reserve range is reached, the fuel reserve warning lamp (A1e4) lights up yellow if the engine is running. (To prevent the lamp from flickering the control signal is transmitted with a delay.)

In the event of a fault, the needle of the fuel level and reserve gauge (A1p2) is moved to "0." The fuel reserve warning lamp (A1e4) is not actuated.

Jammed fuel tank sensor recognition

A jammed sensor is detected when the stepper motor value fails to change by at least a defined value (a - stepper motor) within a certain distance (km threshold). If this state occurs, an appropriate jam error bit is set. The bit is erased when the required stepper motor change has taken place. The variables a-stepper motor and km threshold can be changed, and are stored in EEPROM. The jammed sensor recognition function is deactivated by means of an encoding bit in the EEPROM. The jammed sensor fault is recorded in the fault memory.

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