Fuel Pump Control Unit: Description and Operation
GF47.40-P-2001MMC Component Description For Fuel System Control Unit
- ENGINES 157.9 in MODEL 216.3, 221.0 /1
LH rear compartment shown on model 221
N118 Fuel pump control unit
LocationThe fuel pump control unit is located in the LH rear compartment.
Task
The FSCU has been awarded the internal designation UFPC AMG (Universal Fuel Pump Controller for AMG).
The fuel pump control unit regulates the fuel pump (M3) according to need and transmits information via 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 fuel pump control unit and appropriate output signals are emitted:
- CAN input signals
- CAN output signals
- Direct input signals
- Direct output signals
CAN input signals
- Fuel pump ON
- Data for variant coding
CAN output signals
- Fuel supply status
- Diagnostic data
Direct input signals
- Circuit 15
- Circuit 30
- Circuit 31
- Ground signal "fuel pump ON"
- Sensor signal from fuel pressure sensor (B4/7)
- "Specified fuel pressure" pulse width modulated signal (PWM signal)
Direct output signals
- Power supply for fuel pressure sensor (5 V)
- Fuel ground pressure sensor
- AC signal for fuel pump (phase A)
- AC signal for fuel pump (phase B)
- AC signal for fuel pump (phase C)
Design
The fuel system control unit consists of a fuel housing with two plugs and internal measuring and control electronics.
Function
The function is described at 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 ME-SFI [ME] control unit as a CAN signal via the drive train CAN (CAN C) and directly as a ground signal.
The fuel pump 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 control unit.
To control the fuel pump, the ME-SFI [ME] control unit evaluates the fuel pressure and load requirement and sends the "specified fuel pressure" PWM signal to the fuel pump control unit.
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 the motor rpm between about 4.5 to a maximum of 6.7 bar.
Fuel system control unit limp-home mode
- If the "fuel pump ON" ground signal fails or is implausible, the fuel pump is shut off.
- If the "specified fuel pressure" signal fails or is implausible, the fuel pumps are shut off.
- If the "Circuit 15" signal fails or is implausible, the fuel pump control unit (and therefore the fuel pump) is switched off.
Diagnosis
The fuel system control unit conducts a self-test and a component test. If an error is detected, it is stored by the fuel pump control unit and made available to the ME-SFI [ME] control unit via the drive train CAN and also an attached Diagnosis Assistance System (DAS) via the diagnostic CAN (CAN-D).
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 the DAS, and the following parameters are entered:
- Parameter 01 for "fuel pump ON"
- Time "0-99999" seconds
- Specified fuel pressure 5.5 bar
During emptying the DAS must be connected and the ignition must remain on.
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.
