Component description for fuel pump control unit

P47.40-2071-11

LH rear compartment shown on model 221

N118 Fuel pump control unit

Location

The fuel pump control unit is located in the LH rear compartment.

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 preset specified value of 3.8 bar.

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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

- Terminal 15

- Circuit 30

- Tml. 31

- "Fuel pump ON" ground signal

- Sensor signal from fuel pressure sensor (B4/7)

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Direct output signals

- Fuel pressure sensor + (5 V)

- Fuel pressure sensor -

- Fuel pump + (12 V) (pulse width modulated signal (PWM signal))

- Fuel pump - (PWM signal)

CAN input signals

- Diagnosis requests

- Data for variant coding

CAN output signals

- PWM signal duty cycle (fuel pump actuation
0 to 100 %)

- Self-diagnosis data

- Requested diagnostic data

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Design

The fuel pump 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 pump limp-home mode control unit

 Diagnosis

 Tank-draining function

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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 preset specified value of 3.8 bar, and actuates the fuel pump by means of a PWM signal as required, so that the actual value corresponds to the specified value.

The fuel delivery capacity is up to 145 l/h.

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Fuel pump limp-home mode control unit

- 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 pump control unit conducts an own and component check. Detected faults are stored by the fuel pump control unit and are available over the drive train CAN (CAN C) to the ME-SFI control unit and the Diagnosis Assistance System (DAS) when connected.

Tank-draining function

The fuel tank can be emptied over the fuel pump 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

- Specified 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 pump control unit. After replacing the fuel pump control unit, variant coding must be conducted.