Component description for fuel pump control unit

P47.40-2076-11

View of rear footwell on the left

N118 Fuel pump control unit

Location

The fuel system control unit is located in a rear footwell behind the driver seat.

Task

The fuel pump control unit varies the fuel pressure via the fuel pump (M3) between about 3.6 and 5.0 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 input signals

 CAN output signals

Direct input signals

- Circuit 15

- Circuit 30

- Circuit 31

- "Fuel pump ON" ground signal

- "Specified fuel pressure" pulse width modulated signal (PWM signal)

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Direct output signals

- Fuel pump PWM signal (phase 1)

- Fuel pump PWM signal (phase 2)

- Fuel pump PWM signal (phase 3)

CAN input signals

- Actual fuel pressure

- 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 is described at the following points:

 Fuel pump control

 Emergency running

 Diagnosis

 Tank-draining function

Fuel pump control

The fuel supply is controlled and monitored by the ME-SFI [ME] control unit (N3/10) and fuel pump control unit.

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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.

The ME-SFI [ME] control unit detects the current fuel pressure through the voltage signal from the fuel pressure sensor (B4/7).

To control the fuel pump, the ME-SFI [ME] control unit evaluates the fuel pressure and load requirement and sends the "specified fuel pressure" PWM signal to the fuel pump control unit. This evaluates the PWM signal and actuates the fuel pump with a phase-shifted PWM signal as required, so that the actual fuel pressure value corresponds to the specified value.

Depending on the fuel requirements, fuel pressure is regulated
between about 3.6 and 5.0 bar.

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Emergency running

- If the "fuel pump ON" ground signal fails or is implausible, the fuel pump is shut off.

- If the "specified fuel pressure" signal fails or is implausible, the fuel pump is actuated with continuous fixed PWM signals (for maximum delivery).

- If the "Circuit 15" signal fails or is implausible, the fuel pump control unit (and therefore the fuel pump) is switched off.

Diagnosis

The fuel pump control unit conducts an own and component check. If an error is detected, it is stored by the fuel pump control unit and made available to the ME-SFI [ME] control unit via the diagnostic CAN (CAN D) and engine compartment CAN (CAN C) and an attached Diagnosis Assistance System (DAS).

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 5.0 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 a variant coding must be conducted.