Fuel Pump Control Unit, Component Description - GF47.40-S-2001TRC

Engine 274 in model 447

Engine 274 in model 448

Fig 1: Fuel System/Pump Control Unit Components Location - Model 447 With Engine 274

Courtesy of MERCEDES-BENZ USA

Location

The fuel system control unit (FSCU) (N118) is installed under the driver's seat.

Task

The fuel system control unit (FSCU) (N118) regulates the fuel pump with fill level sensor (M3/6) in accordance with requirements and transmits information about the current fuel pressure to the ME-SFI [ME] control unit (N3/34).

To do this the FSCU (FSCU) (N118) fulfills the following tasks:

Reading in of signals
Evaluation of signals
Output of signals and actuation of assembly parts
Regulation of the fuel pump with fill level sensor (M3/6)
Fill level evaluation of the fuel tank
Emptying the fuel tank
Diagnosis

Reading in of signals

Signals are read in via the following connections:

Direct lines
Drive train CAN (CAN C)

Direct lines

Circuit 15 of firewall fuse and relay module (K40/11)
Circuit 30 of firewall fuse and relay module (K40/11)
"Fuel pump with fill level sensor (M3/6) signal ON" from ME-SFI [ME] control unit (N3/34)
Fuel fill level and fuel pressure from the fuel pump with fill level sensor (M3/6)

Drive train CAN (CAN C)

Fuel pump with fill level sensor (M3/6) ON
Fuel specified pressure

Evaluation of signals

The read in signals are evaluated by the integral microprocessor, and the relevant components are actuated.

Output of signals and actuation of assembly parts

Signals are read in via the following connections:

Direct lines
Drive train CAN (CAN C)

Direct lines

Power supply for the fuel pressure sensor (5 V) integrated in the fuel pump with fill level sensor (M3/6)
Fuel pump ground connection with fill level sensor (M3/6)
Fuel pump AC voltage signal with fill level sensor (M3/6) (Phase U)
Fuel pump AC voltage signal with fill level sensor (M3/6) (Phase V)
Fuel pump AC voltage signal with fill level sensor (M3/6) (Phase W)

Drive train CAN (CAN C)

Fuel pressure
Fuel-tank level
Diagnostic data

Regulation of the fuel pump with fill level sensor (M3/6)

Switching on of the fuel pump with fill level sensor (M3/6) takes place if a respective signal is received by the FSCU (FSCU) (N118). This signal is sent redundantly from the ME-SFI [ME] control unit (N3/34) as a CAN signal via the drive train CAN (CAN C) and directly as a ground signal. The FSCU (FSCU) (N3) detects the current fuel pressure over a signal from an integral fuel pressure sensor in the fuel pump with fill level sensor (M3/6) and transmits this information via the drive train CAN (CAN C) to the ME-SFI [ME] control unit (N118/34). In order to control the fuel pump with fill level sensor (M3/6) the ME-SFI [ME] control unit (N3/34) evaluates the fuel pressure and the engine load request and transmits the CAN signal "fuel specified pressure" to the FSCU (FSCU) (N118). This evaluates the CAN signal and actuates the fuel pump with fill level sensor (M3/6) with a three phase shifted alternating current in such a way that the actual fuel pressure corresponds to the specified value. The fuel pressure is regulated dependent on the fuel temperature and the engine rpm between about 4.5 and 6.7 bar.

Limp-home mode for fuel system control unit (FSCU) (N118):

If the "fuel specified pressure" signal is missing and the signal of the fuel pressure sensor integrated in the fuel pump with fill level sensor (M3/6), the fuel pump with fill level sensor (M3/6) is regulated as per a specified pressure value in the FSCU (FSCU) (N118)
If the CAN signal "fuel pump with fill level sensor (M3/6) ON" and the ground signal "fuel pump with fill level sensor (M3/6) ON" are missing or the signal is implausible, the fuel pump with fill level sensor (M3/6) is switched off
If the CAN signal "circuit 15" and the direct signal "circuit 15" are missing, the FSCU (FSCU) (N118) and therefore also the fuel pump with fill level sensor (M3/6) is switched off

Fill level evaluation of the fuel tank

The FSCU (FSCU) (N118) reads in the signal of the fill level sensor integrated in the fuel pump with fill level sensor (M3/6) for fill level evaluation of the fuel tank.

The current fill level as a percentage and liter is calculated from this signal and the nominal volume of the fuel tank and transmitted as a CAN signal to the ME-SFI [ME] control unit (N3/34). The fill level sensor is also checked for plausibility. In the event of implausible measurements, a fault message is stored in the fault memory and is sent to the ME-SFI [ME] control unit (N3/34) in the form of a fill level 0%.

Emptying the fuel tank

The fuel tank can be emptied over XD and the FSCU (FSCU) (N118) without the engine running.

Diagnosis

The fuel system control unit (FSCU) (N118) performs an own and component check.

Recognized faults are stored by the FSCU (FSCU) (N118) and sent via the drive train CAN (CAN C) to the ME-SFI [ME] control unit (N3/34) and from there via chassis CAN (CAN E), electronic ignition lock control unit (EZS) (N73) and diagnostic CAN (CAN D) to the diagnostic connector (X11).

Body

The FSCU (FSCU) (N118) consists of a plastic housing with two plug couplings and the inner measuring and control electronics.

Power supply

The power supply takes place over circuit 30 and circuit 15 from the firewall fuse and relay module (K40/11).

Ground connection

The ground line connections takes place over the additional battery ground point (W10/4).

Variants

The vehicle and engine variants are already stored in the fuel system control unit (FSCU) (N118). After exchanging the FSCU (FSCU) (N118) a variant coding must be carried out.

	Wiring diagram for FSCU	Engine 274 in model 448	PE47.40-S-2101-97VDA
		Engine 274 in model 448	PE47.40-S-2101-97VDA