ENGINE | 642.896 in MODEL 906 |
N118/5 | Fuel system control unit |
D47.40-0001-03
Location
The fuel system control unit is located under the trim of the right rear door sill.
Task
The fuel system control unit is supplied by the "Continental Automotive GmbH" company and bears the internal designation FSCM (Fuel System Control Module). The fuel system control unit regulates the fuel pump with fill level sensor (M3/5) in accordance with requirements and transmits information about the current fuel pressure to the CDI control unit (N3/30).
Input and output signals
A distinction is made between the following signal paths:
Direct input signals
Direct output signals
Direct input signals
The following signals are read in by the FSCU via discrete lines:
- circuit 15
- circuit 30
- circuit 31
– "Fuel pump ON" (ground)
– fuel pressure signal from fuel pressure sensor (B4/7)
Direct output signals
The FSCU evaluates the read in signals and then actuates the following components in response over discrete lines:
– fuel pump with fill level sensor (12 V) (pulse width modulation (PWM) signal, Plus)
– fuel pump with fill level sensor (PWM signal), Minus)
The FSCU also issues the following signals over discrete lines:
– fuel pressure sensor, power supply (5 V)
– fuel pressure sensor, ground
Body
The fuel system control unit consists of a fuel housing with two plug connections and internal measuring and control electronics.
Function
The function of the FSCU is subdivided into the following points:
Regulation of fuel pump with fill level sensor
Limp-home mode
Diagnosis
Container-draining function
Regulation of fuel pump with fill level sensor
Switching on of the fuel pump with fill level sensor takes place if the signal "fuel pump ON" is received by the fuel system control unit.
The fuel system control unit evaluates the current fuel pressure, compares it with the specified fuel pressure and actuates the fuel pump with fill level sensor 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. 4.25 bars, depending on the fuel requirement.
The maximum feed volume at 12 V supply voltage and loaded fuel filter is 155 l/h.
Limp-home mode
- if the signal "Fuel pump ON" is missing the fuel pump with fill level sensor 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 an own and component check. Recognized errors are stored by FSCU. The faults can be read out via the diagnostic CAN (CAN D) using XD.
container-draining function
The fuel tank can be emptied over the fuel system control unit without the engine running.
To do this, the container draining function is selected using Xentry Diagnostics, and the following parameters are entered:
- "01" for "fuel pump ON"
- time: 0 to 99999 s
– 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 can also be pumped off via a drain pipe.