Component Description For Fuel Pump Control Unit - GF47.40-P-2001MMK

Engine 157.9, 276.8, 278.9 in model 217, 222 

Engine 176.9, 177.9 in model 217 

Engine 176.9, 177.9 in model 222 

Engine 177.9 in model 290 

Engine 256.9 in model 222, 257, 290 

Engine 276.9 in model 222 

Shown on rear bench seat (with model 222) 

Location 

The fuel system control unit is located in the trunk behind the right rear seat above the fuel tank.

Tasks 

The fuel system control unit bears the internal designation FSCM-GEN 4 (F  uel S  ystem Control M  odule G  eneration 4  ).

The fuel system control unit regulates the fuel pump (M3) according to demand and transmits information about the current fuel pressure and the fill level of the fuel tank to the ME-SFI control unit (N3/10).

Input and output signals 

The following input signals are evaluated by the FSCU and the respective output signal is issued:

• Direct input signals 
• Direct output signals 
• CAN input signals via drive train CAN (CAN C1) 
• CAN output signals via drive train CAN 

Direct input signals 

• Circuit 15 signal
• Chassis 30
• Circuit 31
• Ground signal "Fuel pump ON"
• Left fuel tank fuel level indicator fill level sensor signal (B4/1)
• Right fuel tank fuel level indicator fill level sensor signal (B4/2)
• Fuel pressure sensor signal (B4/7)

Direct output signals 

• Power supply for fuel pressure sensor (5 V)
• Ground connection for left fuel tank fuel level indicator fill level sensor
• Fuel tank fuel level indicator fill level sensor ground connection, right
• Fuel pressure sensor ground connection
• Actuation of the fuel pump (Phase U)
• Actuation of the fuel pump (Phase V)
• Actuation of the fuel pump (Phase W)

CAN input signals via drive train CAN 

• Fuel pump ON
• Fuel specified pressure, quantity specification
• Status of engine

• Engine oil temperature
• Engine torque
• Engine speed
• Coolant temperature
• Accelerator pedal position
• Atmospheric pressure

CAN output signals via drive train CAN 

• Fuel pressure
• Diagnostic data
• Fuel tank fill level
• Status of fuel system

Structure 

The fuel system control unit consists of a plastic housing with two connectors, a metal floor panel and inner measuring and control electronics.

Function 

The function is described in the following points:

• Regulation/control of the fuel pump 
• Fuel system control unit limp-home mode 
• Fill level evaluation of fuel tank 
• Diagnosis 
• Tank drainage service 

Regulation/control of the fuel pump 

Switching on of the fuel pump takes place if a "fuel pump ON" signal is received by the FSCU. This signal is transmitted redundantly by the ME-SFI [ME] control unit as a CAN signal via the drive train CAN and directly as a ground signal.

The fuel system control unit detects the current fuel pressure by means of a voltage signal from the fuel pressure sensor and transmits this information via the drive train CAN to the ME control unit.

In order to control the fuel pump the ME-SFI [ME] control unit evaluates the fuel pressure and the load request and adjusts the requested fuel pressure over an integral controller through actuation of the fuel pump.

The low fuel pressure is controlled to between approx. 4 to a maximum of 6.7 bar, depending on the fuel temperature and the engine rpm.

Fuel system control unit limp-home mode 

Limp-home functions for failure of the drive train CAN and the fuel pressure sensor are stored in the FSCU.

• Upon failure of the drive train CAN the signals "fuel pump ON" and "terminal 15" are redundantly sent over a direct line from the ME-SFI [ME] control unit to the FSCU. The fuel pump regulates the pressure to a substitute value stored in the FSCU.
• For failure of the fuel pressure sensor the fuel pump is actuated over fail safe characteristics curve in the FSCU.
• If both the drive train CAN and the fuel pressure sensor fail, the fuel pump according to a voltage stored in the FSCU.

Fill level evaluation of fuel tank 

The FSCU determines the current resistance of the fuel level indicator fuel tank fill level sensor over a voltage measurement and therefore the fill level of the fuel.

The determined voltage value is compared with a characteristic stored in the FSCU which is dependent on the fuel tank volume. The FSCU therefore calculates the contents of the fuel tank and checks this for plausibility with the current fuel consumption of the engine.

The values checked for plausibility are transmitted via the CAN network in liters and percentage to the IC (A1). Upon reaching the reserve quantity a signal is sent to the IC which then issues a warning message.

Diagnosis 

The control unit performs a self and component diagnosis. Recognized faults are stored by the FSCU and made available via the drive train CAN to the Me-SFI [ME] control unit and additionally via the diagnostic CAN (CAN D) to attached diagnostic equipment.

The self and component diagnosis checks all inputs and outputs for short circuits, an on-board electrical system voltage as well as an open circuit. All values of the sensors are also checked for plausibility. The respective limp-home functions are activated for known faults.

Tank drainage service 

The fuel tank can be emptied over the FSCU without the engine running.

To do this, the container draining function is selected using Xentry Diagnostics, and the following parameters are entered:

• Parameter 01 for "fuel pump ON"
• Time "0-99999"s
• Fuel specified pressure 5.5 bar

During emptying the ignition must remain switched on.

Variants 

For adaptation to different vehicle, engine, fuel tank variants and fuel pumps, different parameter sets are stored in the FSCU. For in-service date and exchange of the FSCU the respective parameters must be selected over the variant coding.

	Wiring diagram for FSCU	Engine 177.9 in model 290	PE47.40-P-2101-97XBA
		N118, model 217, 222 up to model year 2018	PE47.40-P-2101-97SEA
		N118, model 217, 222 from model year 2018	PE47.40-P-2101-97SEC