Component description for fuel pump control unit - GF47.40-P-2001MFG
ENGINES 271.958 in MODEL 212.041 with CODE (924) Bivalent natural gas drive
View of right door sill in the rear compartment
Location
The fuel system control unit is located under the trim of the right rear door sill.
Task
The fuel pump control unit is designated internally as FSCM light (F uel S ystem C ontrol M odule light).
The fuel pump control unit regulates the fuel pump (M3) according to need and transmits information via the current fuel pressure to the ME-SFI [ME] control unit (N3/10).
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
- Ground signal "fuel pump ON"
- Fuel pressure sensor, sensor signal (B4/7)
Direct output signals
- Power supply for fuel pressure sensor (5 V)
- Fuel pressure sensor mass
- Fuel pump + (12 V) (pulse width modulated signal (PWM signal)) (Plus)
- Fuel pump (PWM signal) (Minus)
CAN input signals
- Fuel pump ON
- Specified fuel pressure
CAN output signals
- Fuel pressure
- Diagnostic data
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
Switching on of the fuel pump takes place if a signal "fuel pump ON" is received by the fuel system control unit. This signal is sent redundant from the ME-SFI [ME] control unit as a CAN signal via the drive train CAN (CAN C) and as a ground signal.
The fuel pump control unit also receives the CAN signal "nominal pressure of the fuel" from the ME-SFI [ME] control unit.
The fuel pump 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.
The fuel system control unit evaluates the current fuel pressure, compares it with the specified fuel pressure and actuates the fuel pump appropriately by means of a PWM signal in such a way that the actual value of the fuel pressure corresponds to the specified value.
The fuel delivery volume is regulated variably from 0 to 130 l/h for a fuel pressure of about 3.8 bar according to the fuel requirements.
Fuel system control unit limp-home mode
- If the signal "nominal pressure of the fuel" is missing a substitute value is created and the fuel pump is appropriately actuated by the fuel pump control unit.
- If the signal "nominal pressure of the fuel" and the signal from fuel pressure sensor is missing, the fuel pump is actuated by an established permanent pulse width modulation signal (maximum delivery = 130 l/h).
- If both signals "Fuel pump ON" are missing, the fuel pump is actuated upon recognition of circuit 15.
- Various limp-home functions ensure that the fuel supply is also ensured for a failure of the internal control system (e.g. failure of the processor).
Diagnosis
The fuel system control unit conducts a self-test and a component test. Recognized errors are stored by the fuel pump control unit and sent to the Xentry diagnostics via the diagnostic CAN to the ME-SFI control unit via the drive train CAN.
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 Xentry Diagnostics, and the following parameters are entered:
- Parameter 01 for "fuel pump ON"
- Time "0-99999" seconds
- Duty cycle of the PWM signal to 100%
During draining, Xentry Diagnostics must remain connected and the ignition must remain switched 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.
| Designation | Unit | Values | Tolerance range | Remarks | |
|---|---|---|---|---|---|
| Fuel pump control unit (N118) | |||||
| Supply voltage | V | 13.5 | |||
| Voltage limit: | minimum | V | 6.0 | ||
| maximum | V | 16.0 | 27.0 V for a maximum of 1 minute | ||
| Power consumption: | Quiescent current | mA | 0.1 | ||
| mode, | A | 0.3 | |||
| further operation | A | 12.0 | |||
| Ascertain | A | 25 | |||
| Reverse polarity protection | Inverse-polarity protection diode between circuit 30 and circuit 31 | ||||
| Short-circuit resistance | For power supply, load outputs and signal lines | ||||
| Operating temperature range | °C | -40 - 85 | |||
| Diagnosis capability | Yes | ||||
| Flash capability/coding capability | Yes/yes | ||||
| Special features | De-tanking service (de-tanking without engine running) | ||||
| Fuel pressure sensor (B4/7) | |||||
| Model | Capacitive, absolute measuring sensor | ||||
| Supply voltage | V | 5.0 | ±0.25 V | ||
| Signal voltage | V | 0.3-4.5 | Linear, signal proportional to fuel pressure | ||
| Measuring range | bar | 0.5-10 | |||
| Operating temperature range | °C | -40-80 | |||
| Fuel pump (M3) | |||||
| Model | Two-stage flow pump HPI 4.6 | ||||
| Supply voltage | V | 12.0 | PWM signal from fuel pump control unit (N118) | ||
| Delivery rate maximum | l/h | 130 | |||
| Wiring diagram for fuel system control unit | N118 | PE47.40-P-2101-97DAA |