Fuel Pump Control Unit: Description and Operation

GF47.40-P-2001MIG Component Description For Fuel System Control Unit
- ENGINES 272.945 in MODEL 251.054 /154 as of model year 2009 / CY 08
- ENGINES 272.967 in MODEL 164.186 as of model year 2009 /CY 08 model refinement package
- ENGINES 272.967 in MODEL 251.056 /065 /156 /165 as of model year 2009 / CY 08
- ENGINES 273.923 in MODEL 164.871 as of model year 2009 / CY 08
- ENGINES 273.963 in MODEL 164.172 as of model year 2009 /YoM 08 model refinement package
- ENGINES 273.963 in MODEL 164.886, 251.072 /172 as of model year 2009 / CY 08





Shown on right rear seat, model 164
N118 Fuel pump control unit

Location
The fuel system control unit is located on the right below the rear seat.





Shown on right rear football, model 251
N118 Fuel pump control unit

Location
The fuel pump control unit is located in the rear footwell on the right.

Task
The fuel pump control unit is supplied by "Siemens VDO Automotive AG" and carries the internal designation FSCM light (Fuel System Control Module light).

The fuel pump control unit sets the fuel pressure via the fuel pump (M3) to the specified value of 3.8 bar.

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 signals from fuel pump control unit
- CAN signals to fuel pump control unit

Direct input signals
- Circuit 15
- Terminal 30
- Circuit 31
- Signal "Fuel pump ON"
- Sensor signal from fuel pressure sensor (B4/7)

Direct output signals
- Fuel pressure sensor + (5 V)
- Fuel pressure sensor -
- Fuel pump +
- Fuel pump -

CAN signals from fuel pump control unit
- Diagnostic data

CAN signals to fuel pump control unit
- Diagnosis requests

Design
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
The fuel pump is switched on when the fuel pump control unit receives the "fuel pump ON" ground signal directly from the ME-SFI [ME] control unit (N3/10).
The fuel pump control unit detects the current fuel pressure through the voltage signal from the fuel pressure sensor.
The fuel pump control unit evaluates the current fuel pressure, compares it with the specified value of 3.8 bar, and actuates the fuel pump with a pulse width modulated signal (PWA signal) as required, so that the actual value corresponds to the specified value. The fuel delivery capacity is up to 145 l/h.

Fuel system control unit limp-home mode
- To ensure security of fuel supply, the fuel pump control unit has a limp-home function, which is activated if there is an internal control system failure (for example, a processor fault).
- If the signal from the fuel pressure sensor is missing, the fuel pump is actuated by means of an established permanent PWM signal (maximum delivery).
- If the signal "Fuel pump ON" in missing the fuel pump is actuated upon recognition of "terminal 15".

Diagnosis
The fuel system control unit conducts a self-test and a component test. Detected faults are stored by the fuel pump control unit and are available over the diagnostic CAN (CAN C) to the ME-SFI [ME] control unit and the Diagnosis Assistance System (DAS) when connected.

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 the DAS, and the following parameters are entered:
- Parameter "01" for "fuel pump ON"
- Time "0-99999" seconds
- Fuel pressure 3.8 bar

During emptying the DAS must be connected and the ignition must remain 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.