Component description for fuel pump control unit - GF47.40-P-2001MRB

ENGINE 274.9 in MODEL 207, 218 

ENGINE 274.9 in MODEL 212 without CODE 924 (Bivalent natural gas drive) 

View of right inside side wall (for model 207) 

Fig 1: Fuel System Control Unit - Shown On Model 207

Courtesy of MERCEDES-BENZ USA

Location 

For model 207 the FSCU is located under the rear bench seat in the area of the right sidewall.

View of right rear compartment door sill (for model 212, 218) 

Fig 2: Fuel System Control Unit - Shown On Model 212

Courtesy of MERCEDES-BENZ USA

Location 

On model 212 and model 218, the fuel system control unit is located below the paneling on the right rear door sill.

Task 

The FSCU carries the internal designation FSCM-EC (F  uel S  ystem C  ontrol M  odule for E  lectronically C  ommutated fuel pumps).

The FSCU controls the fuel pump according to need (M3) and transmits information about the current fuel pressure 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 
• CAN output signals 

Direct input signals 

• Terminal 15
• Terminal 30
• Circuit 31
• "Fuel pump ON" ground signal
• Fuel pressure sensor signal (model, 207, 212) or fuel pressure sensor (model 218) (B4/7)

Direct output signals 

• Fuel pressure sensor power supply (5 V)
• Fuel pressure sensor ground connection
• 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 

• Fuel pump ON
• Fuel specified pressure

CAN output signals 

• Fuel pressure
• Diagnostic data

Body 

The fuel system control unit consists of a fuel housing with two plug connections and internal measuring and control electronics.

Function 

The function is described in the following points:

• Controlling the fuel pump 
• Fuel system control unit limp-home mode 
• Diagnosis 
• Tank drainage service 

Controlling 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 sent redundant from the ME-SFI [ME] control unit as a CAN signal via the drive train CAN (CAN C) and as a ground signal.

The fuel system control unit also receives the CAN signal "specified pressure of the fuel" from the ME-SFI [ME] control unit.

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-SFI [ME] control unit.

The fuel system control unit evaluates the current fuel pressure, compares it with the fuel specified pressure and actuates the fuel pump appropriately by means of these phase-offset AC voltage signals in such a way that the actual value of the fuel pressure corresponds to the specified value.

The fuel pump pressure is controlled dependent on the fuel temperature and the engine RPM between about 4.5 to a maximum of 6.7 bar.

Fuel system control unit limp-home mode 

If the signal "specified pressure of the fuel" is missing a substitute value is created and the fuel pump is appropriately actuated by the fuel system control unit.

If the "Fuel specified pressure" signal and the signal from the fuel pressure sensor are missing, the fuel pump is regulated as per a specified pressure value stored in the fuel system control unit.

Over the direct signals "fuel pump ON" and "circuit 15" the limp-home function ensures that the fuel supply is also secured for failure of the internal control system.

Diagnosis 

The FSCU performs am own and component check. 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.

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" seconds
• Fuel specified pressure 5.5 bar

During draining, Xentry Diagnostics must remain connected and the ignition must remain switched on.

Variants 

The vehicle and engine variants are already stored in the FSCU. After replacement of the FSCU a variant coding must be carried out.