Shown: Model 205.0 |
N118 | Fuel system control unit |
P47.40-2119-76
Location
The fuel system control unit is located under the trim of the right rear rocker panel.
Tasks
The fuel system control unit is supplied by the Continental Automotive GmbH company and bears the internal designation FSCM (GEN4Fuel System Control Module Generation 4).
The fuel system control unit regulates the fuel pump (M3) in accordance with requirements 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 FSCU and the respective output signal is issued:
Direct input signals
Direct output signals
CAN input signals
CAN output signals
Direct input signals
Terminal 15
Circuit 30
Circuit 31
Fuel pump signal ON
Fuel tank fuel level indicator fill level sensor, left (B4/1) (with code 916 (Fuel tank 66 l))
Right fuel tank fuel level indicator fill level sensor (B4/2)
Fuel pressure sensor signal (B4/7)
Direct output signals
Power supply for fuel pressure sensor (5 V)
Ground connection for left fuel tank fuel level indicator fill level sensor
Fuel tank fuel level indicator fill level sensor ground connection, right
Fuel pressure sensor ground connection
Alternating voltage signal for fuel pump (Phase U)
Alternating voltage signal for fuel pump (Phase V)
Alternating voltage signal for fuel pump (Phase W)
CAN input signals
Fuel pump ON
Fuel specified pressure
CAN output signals
Fuel pressure
Diagnostic data
Structure
The fuel system control unit consists of a fuel housing with two plug connections and internal measuring and control electronics.
Function
The function description is subdivided into the following points:
Controlling the fuel pump
Fuel system control unit limp-home mode
Fill level evaluation of fuel tank
Diagnosis
Tank drainage service
Variants
Controlling the fuel pump
Switching on of the fuel pump takes place if a "fuel pump ON" signal is received by the FSCU. This signal is sent redundantly by the CDI control unit as a CAN signal via the drive train CAN (CAN C1) and directly as a ground signal. The fuel system 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 CDI control unit. In order to control the fuel pump the CDI control unit evaluates the fuel pressure and the load request and transmits the pulse width modulated signal "fuel specified pressure" to the FSCU. This evaluates the PWM signal and actuates the fuel pump with a phase-shifted alternating current as required, so that the actual fuel pressure corresponds to the specified value. The fuel pump pressure is regulated dependent on the fuel temperature and engine rpm to between approx. 4.5 up to a maximum of 6.7 bar.
Fuel system control unit limp-home mode
If the ground signal "fuel pump ON" is missing or it is implausible, the fuel pump is switched off.
If the "fuel specified pressure" signal fails or is implausible, the fuel pumps are shut off.
If the "circuit 15" signal fails or is implausible, the fuel system control unit and therefore the fuel pump is switched off.
Fill level evaluation of fuel tank
The FSCU reads signals from the fuel tank fuel level indicator fill level sensor to compute and evaluate the fill level of the fuel tank.
The nominal volumes of the fuel tank, the current fill level in percent and the reserve quantity are calculated from the values measured in ohms and transmitted to the CDI control unit with an appropriate signal. Furthermore the fill level sensors are checked for plausibility. In the event of implausible measurements, a fault message is sent to the CDI control unit.
Diagnosis
The FSCU performs am own and component check.
Recognized faults are stored by the FSCU and made available via the drive train CAN to the CDI control unit and additionally via the diagnostic CAN (CAN D) to attached diagnostic equipment.
Tank drainage service
The fuel tank can be emptied over the FSCU without the engine running. To do this, the container draining function is selected using Xentry Diagnostics, and the following parameters are entered:
Parameter 01 for fuel pump ON
Time "0-99.999" seconds
Specified fuel pressure 5.5 bar
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 FSCU. After replacement of the FSCU a variant coding must be carried out. The fuel system control unit is Star2-capable.