Component description for fuel pump control unit - GF47.40-P-2001MNA
ENGINE 177.9 in MODEL 205
Shown: entrance to the right rear
Location
The fuel system control unit is located in the door sill next to the right rear seat.
Task
The fuel system control unit bears the internal designation FSCM-GEN 4 (F uel S ystem C ontrol 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 [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)
- CAN output signals via drive train CAN
Direct input signals
- Circuit 15 signal
- Terminal 30
- Circuit 31
- "Fuel pump ON" ground signal
- 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 signal (B4/7)
Direct output signals
- Fuel pressure sensor power supply (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 fuel pump (Phase U)
- Actuation of fuel pump (Phase V)
- Actuation of fuel pump (Phase W)
CAN input signals via drive train CAN
- Fuel pump ON
- Fuel specified pressure
- Status of engine
- Engine torque
CAN output signals via drive train CAN
- Fuel pressure
- Diagnostic data
- Fuel tank fill level
- Status of fuel system
Body
The FSCU consists of a plastic housing with two plug couplings and the inner measuring and control electronics.
Function
The function is described in the following points:
- Controlling the fuel pump
- Fuel system control unit limp-home mode
- Fill level evaluation of fuel tank
- 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 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.
To control the fuel pump, the ME-SFI [ME] control unit evaluates the fuel pressure and load requirement and sends the "fuel specified pressure" pulse width modulated signal to the fuel system control unit.
This evaluates the PWM signal and actuates the fuel pump with three phase-shifted alternating current as required, so 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
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.
- Upon failure of the fuel pressure sensor the fuel pump 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 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 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 "0-99.999" seconds
- Fuel specified pressure 5.5 bar
During draining, Xentry Diagnostics must remain connected and 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 | N118 | PE47.40-P-2101-97FBA |