Component description for fuel pump control unit - GF47.40-P-2001OLH

ENGINE 651.924 in MODEL 212.098/298 

View of right door sill in the rear compartment 

Fig 1: Fuel Pump Control Unit

Courtesy of MERCEDES-BENZ USA

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-light (F  uel S  ystem C  ontrol M  odule-light).

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 fuel pump control unit and appropriate output signals are emitted:

• Direct input signals 
• Direct output signals 
• CAN input signals 
• CAN output signals 

Direct input signals 

• Circuit 15
• Circuit 30
• Circuit 31
• "Fuel pump ON" ground signal
• Fuel pressure sensor, sensor signal (B4/7)

Direct output signals 

• Power supply for fuel pressure sensor (5 V)
• Fuel pressure sensor ground
• Fuel pump (12 V) (pulse width modulated signal (PWM signal)) (Plus)
• Fuel pump (PWM signal) (minus)

CAN input signals 

• Fuel pump ON
• Specified fuel pressure

CAN output signals 

• Fuel pressure
• Diagnostic data

Body 

The fuel system control unit consists of a fuel housing with two plugs and internal measuring and control electronics.

Function 

The function description is subdivided into the following points:

• Fuel pump actuation 
• Fuel system limp-home mode control unit 
• Diagnosis 
• Tank-draining function

Fuel pump actuation 

Switching on of the fuel pump takes place if the signal "fuel pump ON" is received by the FSCU from the CDI control unit. This signal is transmitted once redundantly directly as a ground signal and once via the drive train CAN (CAN C). The fuel pump control unit also receives the CAN signal "nominal pressure of the fuel" from the CDI control unit via the drive CAN.

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. The fuel system control unit evaluates the current fuel pressure, compares it with the specified fuel pressure and actuates the fuel pump appropriately by means of a PWM signal in such a way that the actual value of the fuel pressure corresponds to the specified value.

Depending on the fuel requirement, fuel pressure is varied from about 4.0 bar.

The maximum feed volume at 12 V supply voltage and charged fuel filter is 155 l/h.

Fuel system limp-home mode control unit 

• If the signal "Specified fuel pressure" is missing, a substitute value is created by the fuel system control unit and the fuel pump is appropriately actuated.
• If the signal from the fuel pressure sensor is missing, the fuel pump is actuated with a defined permanent PWM signal (maximum delivery).
• If the signal "specified fuel pressure" and the signal from the fuel pressure sensor are missing, the fuel pump is actuated by an established replacement voltage.
• Various limp-home functions ensure that the fuel supply is also provided if the internal controller fails (e.g. processor failure).

Diagnosis 

The fuel pump control unit conducts an own and component check. Recognized errors are stored by the fuel system control unit and sent to Xentry Diagnostics via the diagnostic CAN to the CDI control unit via the drive train CAN.

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 Xentry

Diagnostics, and the following parameters are entered:

• Parameter 01 for "Fuel pump ON"
• Time "0-99999" seconds
• Duty cycle of the PWM signal to 100 %

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 fuel system control unit. After replacing the fuel system control unit, variant coding must be conducted.