View of rear bench seat in model 246 |
N118 | Fuel pump control unit |
P47.40-2113-06
Location
The fuel system control unit is located on the crossmember under the rear bench seat.
On vehicles up to model year 2016 one suspension CAN is present independently of the equipment.
On vehicles as of model year 2016 one suspension CAN is present depending on equipment installed.
Variant 1
If the vehicle does not have equipment codes named in variant 2, one suspension CAN (CAN E) is present as up to model year 2016.
Variant 2
If the vehicle has one of the following equipment codes, there are two chassis CAN (chassis CAN 1 (CAN E2) chassis CAN 2 (CAN E1)) present:
Code 218 (Reversing camera)
Code 234 (Blind Spot Assist)
Code 459 (Steel suspension with adjustable damping)
Code 475 (Tire pressure monitor)
Code 476 (Lane Keeping Assist)
Code 513 (Speed Limit Assist)
Code 614 (Bi-xenon headlamps)
CODE 615 (Bi-xenon headlamp with active curve lights)
CODE 618 (Bi-xenon headlamp)
Code 621 (Intelligent Light System (left-hand traffic))
Code 622 (Intelligent Light System)
Code 631 (Static LED headlamps for left-hand traffic system)
Code 632 (Static LED headlamps for right-hand traffic system)
Tasks
The fuel system control unit bears the internal designation FSCM-light (Fuel System Control Module-light).
The FSCU controls the fuel pump according to need (M3) and transmits information about 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 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
Chassis 30
Circuit 31
"Fuel pump ON" ground signal
Fuel pressure sensor sensor signal (B47)
Direct output signals
Fuel pressure sensor power supply (5 V)
Fuel pressure sensor ground connection
Fuel pump (12 V) (pulse width modulated signal) (plus)
Fuel pump (circuit 31)
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 is described in the following points:
Controlling the fuel pump
Fuel system control unit limp-home mode
Diagnosis
Tank drainage service
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 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 system control unit also receives the CAN signal "specified pressure of the fuel" from the ME-SFI [ME] control unit.
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 ME-SFI [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 accordingly by means of a pulse width modulated signal in such a way that the actual value corresponds to the specified value. Depending on the fuel requirements, fuel pressure is regulated variably between about 4.5 to 6.7 bar.
Fuel system control unit limp-home mode
If the signal "fuel specified pressure" is missing a substitute value is created and the fuel pump is appropriately actuated by the fuel system control unit.
If the signal from the fuel pressure sensor is missing, a consumption-specific limp-home mode characteristic is used to actuate the fuel pump.
If the "Fuel specified pressure" signal and the signal from the fuel pressure sensor are missing, the fuel pump is actuated with a defined substitute voltage.
Diagnosis
The FSCU performs am own and component check. If an error is detected, it is stored by the fuel system control unit and made available to the ME-SFI [ME] control unit via the drive train CAN and also to an attached Xentry Diagnostics via the chassis CAN or via the chassis CAN 1 and the diagnostic CAN (CAN D).
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 to 99.999" s
Fuel specified 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.
Designation | Unit | Values | Tolerance range | Comment |
Fuel system control unit (N118) | ||||
Voltage supply | V | 13.5 | ||
Voltage limit values: minimum maximum | V | 6.0 | 1 min. | |
Power consumption: No-load current operation, additional operation | MA | 0.1 | ||
Ascertain | A | 25 | ||
Pole reverse 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 | |||
Flashability/codablity | Yes/yes | |||
Special features | Tank drainage service (tank drainage with the 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 | Straight-line, a proportional signal to the fuel pressure | |
Measuring range | bar | 0.5 ... 10 | ||
Operating temperature range | °C | -40 ... 80 | ||
Fuel pump (M3) | ||||
Model | Two-stage suction jet pump HPI 4.6 | |||
Supply voltage | V | 12.0 | Pulse width modulated signal from the fuel system control unit | |
Delivery rate at maximum | l/h | 103 |