Fuel Pump Control Unit: Description and Operation
GF47.40-P-2001OM Component Description For Fuel System Control Unit
ENGINES 642.8 as of 1.9.09 in MODELS 212.0/2
View of right rear compartment door sill, on model 204
N118 Fuel pump control unit
Location
The fuel system control unit is located under the trim of the right rear door sill.
Shown: rear seat area without rear bench seat on model 207
N118 Fuel pump control unit
Location
The fuel system control unit is located in the middle under the rear bench seat.
View of right rear compartment door sill, on model 212.0
N118 Fuel pump control unit
Location
On model 212 and model 218, the fuel pump control unit is located below the paneling on the right rear door sill.
Task
The fuel system control unit is supplied by "Continental Automotive GmbH" and carries the internal designation FSCM-light (Fuel System Control Module-light).
The fuel system control unit regulates the fuel pump (M3) according to need and transmits information about the current fuel pressure to the CDI control unit (N3/9).
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 signal (B4/7) (model 204, 207, 212) or fuel pressure sensor (B4/7) (model 218)
Direct output signals
- Power supply (5 V) fuel pressure sensor or fuel pressure sensor
- Fuel pressure sensor or fuel pressure sensor ground
- 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 redundantly from the CDI control unit as a CAN signal via the drive train CAN (CAN C) and as a ground signal. The fuel system control unit also receives the CAN signal "fuel requirements" from the CDI control unit.
The FSCU detects the current fuel pressure based in the voltage signal from fuel pressure sensor or fuel pressure sensor and transmits this information via the drive train CAN to the CDI control unit. The fuel system control unit evaluates the current fuel pressure, compares it with the specified fuel pressure and actuates the fuel pump by means of a PWM signal in such a way that the actual value corresponds to the specified value. In this manner, the fuel pressure is regulated to approx. 4.0 bars, depending on the fuel requirement.
The maximum feed volume at 12 V supply voltage and charged fuel filter is:
- 165 l/h with engine 642.8
- 180 l/h with engine 651.913/925
- 155 l/h with engine 651.9 except 651.913/925
Fuel system control unit limp-home mode
- If the signal "fuel requirements" is missing a substitute value is created and the fuel pump is appropriately actuated by the fuel system control unit.
- If the signal "fuel requirements" and the signal from fuel pressure sensor or fuel pressure sensor are missing, the fuel pump is actuated by an established permanent pulse width modulation signal (maximum delivery).
- 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 system control unit and sent to Xentry Diagnostics via the diagnostic CAN to the CDI 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.
For vehicles as of 06/10 there is a powerful heating element rated at 600 watts installed in the fuel filter. The condensate which has gathered in the fuel filter an also be pumped off via a drain pipe.
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.
