Model 222 |
N118 | Fuel pump control unit |
P47.40-2117-76
Location
The fuel system control unit is located behind the seat backrest of the right rear seat.
Model 213, 257, shown on model 213 |
N118 | Fuel pump control unit |
P47.40-2146-04
Location
The fuel system control unit is located on the right below the rear bench.
Model 238 |
N118 | Fuel pump control unit |
P47.40-2142-11
Location
The fuel system control unit is located on the right rear side wall behind the trim.
Task
The fuel system control unit bears the internal designation FSCMGEN4 (Fuel System Control Module Generation 4).
The fuel system control unit regulates the delivery rate of the fuel pump (M3). To do so, the fuel system control unit evaluates various input signals.
Input signals via direct lines
The fuel system control unit reads in the following signals via direct lines:
Signal "Fuel pump ON"
Sensor signal from fuel tank fuel level indicator fill level sensor, left (B4/1)
Sensor signal from fuel tank fuel level indicator fill level sensor, right (B4/2)
Fuel pressure sensor signal (B4/7) (engine 642, 651)
Input signals via CAN
The fuel system control unit receives, for example, the following signals via the drive CAN (CAN C1):
Terminal status of terminal 15
Fuel system ON
Specified fuel pressure (engine 642, 651)
Volume request (engine 656)
Engine running status
Engine torque
On-board electrical system status
Accelerator pedal position
The fuel system control unit evaluates all relevant input signals and actuates the fuel pump with three phase-offset AC voltage signals:
Alternating voltage phase U
Alternating voltage phase V
Alternating voltage phase W
Output signals via CAN
The fuel system control unit transmits, for example, the following signals via the drive CAN:
Fuel pressure
Fuel pump status
Fuel tank fill level
Status of fuel system
Diagnostic data
After the fuel system control unit has been exchanged, variant coding must be carried out.
Controlling the fuel pump
Switching on of the fuel pump takes place if the signal "fuel pump ON" is received by the fuel system control unit. This signal is transmitted redundantly from the CDI control unit (N3/9) via the drive CAN and as a direct signal.
Pressure control (engine 642, 651)
The fuel system control unit records the current fuel pressure via the signal from the fuel pressure sensor. The fuel system control unit transmits this information to the CDI control unit. The CDI control unit evaluates the fuel pressure and the current load requirement and calculates the specified fuel pressure. The CDI control unit then transmits the specified fuel pressure to the fuel system control unit. The fuel system control unit actuates the fuel pump accordingly with three phase-offset AC voltage signals.
Volume control (engine 656)
The CDI control unit evaluates the current load requirement and transmits a volume request to the fuel system control unit. The fuel system control unit adjusts the requested volume on the basis of an integrated characteristics map. The fuel system control unit actuates the fuel pump accordingly with three phase-offset AC voltage signals.
The fuel pump pressure is regulated depending on the fuel temperature and the engine speed in the following pressure ranges:
Engine 642, 651: approx. 3 to max. 5 bar (absolute pressure)
Engine 656: approx. 4.5 to max. 5.5 bar (absolute pressure)
Limp-home mode
The fuel system control unit switches off the fuel pump under the following conditions:
Circuit status of circuit 15 missing or implausible
"Fuel pump ON" request from CDI control unit missing or implausible
Specified fuel pressure request (engine 642, 651) or fuel volume request (engine 656) from CDI control unit missing or implausible
Fuel tank fill level
The fill level in the fuel tank is recorded by the fuel display fuel tank fill level sensors. The fuel system control unit reads in the signals from the fuel display fuel tank fill level sensors directly and calculates the fill level in the fuel tank. The fill level in the fuel tank is calculated as a percentage. In the case of implausible measurement values, the fuel system control unit transmits a fault message to the CDI control unit.
Tank drainage service
The fuel tank can be emptied without the engine running. In order to do this, the tank draining service must be called up using the diagnostic tester and the following parameters must be entered:
Parameter 01 for fuel pump ON
Time: 0 to 99,999 s
Specified fuel pressure 5 bar
During draining, the diagnostics tester must remain connected and the ignition must remain switched on.