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

Engine 276.8 in model 205, 253 

Shown: Model 205.0 

Location 

The fuel system control unit is located under the trim of the rear right door sill.

Tasks 

The fuel system control unit bears the internal designation FSCM-GEN 4 (F  uel S  ystem C  ontrol M  odule GEN  eration 4  ).

The fuel system control unit regulates the fuel pump (M3) in accordance with the requirements and transmits the information about the current fuel pressure and the fill level of the fuel tank to the ME-SFI [ME] 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 

• Ground signal "fuel system ON"
• Sensor signal from fuel tank fuel level indicator fill level sensor, left (B4/1)
• Sensor signal from fuel tank fuel level indicator fill level sensor, right (B4/2)
• Fuel pressure sensor, sensor signal (B47)

Direct output signals 

• AC voltage signal for fuel pump (Phase U)
• AC voltage signal for fuel pump (Phase V)
• AC voltage signal for fuel pump (Phase W)

CAN input signals via drive train CAN (example) 

• Terminal status of terminal 15
• Fuel system ON
• Fuel specified pressure
• Status of engine
• Engine torque
• On-board electrical system status
• Accelerator pedal position

CAN output signals via drive train CAN (example) 

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

Controlling the fuel pump 

The fuel system control unit actuates the fuel system as soon as it receives the "Fuel system ON" request from the ME-SFI [ME] control unit via drive train CAN or as a direct ground signal.

The fuel pressure is recorded by the fuel pressure sensor. The FSCU directly reads in the signals from the fuel pressure sensor and transmits this information about the fuel pressure to the ME-SFI [ME] control unit via the drive train CAN. The ME-SFI control unit evaluates the fuel pressure and the load requirement. Then, it transmits a pulse width modulated signal (fuel specified pressure) to the fuel system control unit via a direct line and redundantly via the drive CAN. The fuel system control unit actuates the fuel system accordingly with three phase-offset AC voltage signals.

The fuel system control unit controls the fuel system pressure depending on the fuel temperature and the engine rpm between 4.5 to 6.7 bar.

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.

• If the drive train CAN fails, the fuel system control unit merely evaluates the "Fuel system ON" request that is sent by the ME-SFI [ME] control unit via the direct line. The fuel system then sets the fuel system pressure to a stored substitute value.
• If the fuel pressure sensor fails, the fuel system is actuated over a pressure/rpm characteristics map stored in the FSCU.
• If both the drive train CAN and the fuel pressure sensor fail, the fuel pump according to an rpm stored in the FSCU.

Fill level evaluation of fuel tank 

The fuel system control unit reads in the signals of the fuel display fuel tank fill level sensors for the calculation and evaluation of the fill level of the fuel tank.

Furthermore the fill level sensors are checked for plausibility. In a case of implausible measurement values a fault message is sent to the ME-SFI [ME] control unit.

Diagnosis 

The FSCU performs am own and component check. Known faults are stored by the fuel system control unit and transmitted to the ME-SFI control unit and powertrain control unit (N127) via the drive CAN. Known faults are additionally transmitted to a connected diagnostic device via the drive CAN, electronic ignition lock control unit (N73), and diagnostics CAN (CAN D).

Tank drainage service 

The fuel tank can be emptied over the FSCU without the engine running. In order to do this, the tank draining service must be called up using the diagnostic unit and the following parameters entered:

• Parameter 01 for "fuel pump ON"
• Time "0-99.999" s
• Fuel specified pressure 5.5 bar

During emptying the diagnostic unit must be connected and the ignition must remain 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 276.8 in model 205 up to model year 2019 Engine 276.8 in model 253	PE47.40-P-2101-97FBA
		Engine 276.8 in model 205 as of model year 2019	PE47.40-P-2101-97FBB