Component Description For Fuel Pump Control Unit - GF47.40-P-2001MRH
Engine 274.9 in model 205.047/053/054/147/247/253, 253.354/954
Vehicle view from the right rear
Location
The fuel system control unit is located under the trim of the right rear door sill.
Task
The fuel system control unit has the internal designation FSCM-GEN4 F uel S ystem C ontrol M odule GEN eration 4 .
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
- Circuit 30
- Circuit 31
- "Fuel pump ON" ground signal
- Left fuel tank fuel fill level sensor fuel level indicator (B4/1)
- Right fuel tank fuel level indicator fill level sensor (B4/2)
- Fuel pressure sensor (B4/7)
Direct output signals
- Fuel pressure sensor power supply (5 V)
- Fuel pressure sensor ground connection
- Ground connection for left fuel tank fuel level indicator fill level sensor
- Fuel tank fuel level indicator fill level sensor ground connection, right
- 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
- Fuel tank fill level
- Diagnostic data
Structure
The fuel system control unit consists of a plastic housing with two plug connections and internal measuring and control electronics.
Function
The function is described in the following points:
- Controlling the fuel pump
- Fill level evaluation of fuel tank
- 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 redundantly by the ME-SFI [ME] control unit as a CAN signal via the drive train CAN (CAN C1) 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 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.
Fill level evaluation of fuel tank
The FSCU reads signals from the fuel tank fuel level indicator fill level sensor to compute and evaluate the fill level of the fuel tank.
The nominal volumes of the fuel tank, the current fill level in percent and the reserve quantity are calculated from the values measured in ohms and transmitted to the ME-SFI [ME] control unit with an appropriate signal.
Furthermore the data of the fill level sensors is checked for plausibility. In a case of implausible measurement values a fault message is sent to the ME-SFI [ME] control unit.
Fuel system control unit limp-home mode
- If the signal "fuel specified pressure" is missing a substitute value is created and the fuel pump is appropriately actuated by the fuel system control unit.
- If the "specified pressure of the fuel" 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. Detected faults are saved by the fuel system control unit and sent via the drive train CAN, the ME-SFI [ME] control unit and the powertrain control unit (N127), and also via the chassis FlexRay (Flex E) to the electronic ignition lock control unit (N73) and the diagnostic CAN (CAN D) to the connected Mercedes' Xentry Diagnostics device.
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 Mercedes' Xentry Diagnostics device, and the following parameters are entered:
- Parameter 01 for "fuel pump ON"
- Time "0-99.999" s
- Fuel specified pressure 5.5 bar
During draining, the Mercedes' 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.
| Wiring diagram for FSCU | N118 | PE47.40-P-2101-97FBA |