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

ENGINE 274.9 in MODEL 212 with CODE 924 (Bivalent natural gas drive) 

View of right door sill in the rear compartment 

Location 

Fig 1: Fuel Pump Control Unit

Courtesy of MERCEDES-BENZ USA

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

Task 

The fuel system control unit bears the internal designation FSCM-(F  uel S  ystem C  ontrol M  odule for E  lectronically C  ommutated fuel pumps).

The fuel pump control unit regulates the fuel pump (M3) according to need and transmits information via 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 fuel pump control unit and appropriate output signals are emitted:

• Direct input signals 
• Direct output signals 
• CAN input signals 
• CAN output signals 

Direct input signals 

• Circuit 15
• Circuit 30
• Circuit 31
• "Fuel pump ON" ground signal
• Fuel pressure sensor, sensor signal (B4/7)

Direct output signals 

• Power supply for fuel pressure sensor (5 V)
• Fuel pressure sensor ground
• Fuel pump mass
• 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
• Specified fuel pressure

CAN output signals 

• Fuel pressure
• Diagnostic data

Body 

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

Function 

The function description is subdivided into the following points:

• Fuel pump regulation 
• Fuel system limp-home mode control unit 
• Diagnosis 
• Tank-draining function 

Fuel pump regulation 

Switching on of the fuel pump takes place if a signal "fuel pump ON" is received by the fuel system control unit. 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 pump control unit also receives the CAN signal "nominal pressure of the fuel" from the ME-SFI [ME] control unit.

The fuel pump 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 specified fuel pressure and actuates the fuel pump appropriately by means of these phase-offset AC voltage signals in such a way that the actual value corresponds to the specified value.

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

Fuel system limp-home mode control unit 

• If the signal "Specified fuel pressure" is missing, a substitute value is created by the fuel system control unit and the fuel pump is appropriately actuated.
• 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 fuel pump control unit conducts an own and component check.

Recognized errors are stored by the fuel pump control unit and sent to the Xentry diagnostics via the diagnostic CAN to the ME-SFI control unit via the drive train CAN.

Tank-draining function 

The fuel tank can be emptied over the fuel system control unit without the engine running.

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

• Parameter 01 for "Fuel pump ON"
• Time "0-99999" seconds
• Duty cycle of the PWM signal to 100 %

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 fuel system control unit. After replacing the fuel system control unit, variant coding must be conducted.