Fuel Pump Control Unit: Description and Operation
GF47.40-P-2001MAW Component Description For Fuel Pump Control Unit
- ENGINES 156.985 in MODEL 204.077 /277
View of rear compartment from right
N118/3 Left fuel pump control unit
Location
The LH fuel pump control unit is located under the trim of the right rear door sill.
View of trunk from right
N118/4 Right fuel pump control unit
Location
The RH fuel pump control unit is located at the top right of the trunk.
Task
The fuel pump control modules are designated internally as FSCM DECOS (Fuel System Control Module DECOS).
The LH fuel pump control unit controls the LH fuel pump (M3/2) and the RH fuel pump control unit controls the RH fuel pump (M3), according to requirements.
Input and output signals
The fuel pump control units evaluate the following input signals and send the corresponding output signals:
- Direct input signals
- Direct output signals
- CAN input signals
- CAN output signals
Direct input signals
- Terminal 15
- Circuit 30
- Tml. 31
- "Fuel pump ON" ground signal
- "Specified fuel pressure" pulse width modulated signal (PWM signal)
Direct output signals
- Fuel pump +
- Fuel pump -
CAN input signals
- Diagnosis requests
- Data for variant coding
CAN output signals
- Fuel supply status
- Self-diagnosis data
- Requested diagnostic data
Design
Each fuel pump control unit consists of a plastic housing with two plug couplings and internal measurement and control electronics.
Function
The function is described at the following points:
- Fuel pump control
- Emergency running
- Coding
- Tank-draining function
- Diagnosis
Fuel pump control
The fuel supply is controlled and monitored by the ME-SFI control unit (N3/10) and the LH and RH fuel pump control units.
The fuel pumps are switched on if the fuel pump control units receive the "Fuel pump ON" ground signal from the ME-SFI control unit.
The ME-SFI control unit registers the current fuel pressure using the fuel pressure sensor (B4/15). To control the fuel pumps, the ME-SFI control unit evaluates the fuel pressure and required load and sends the "specified fuel pressure" PWM signal (with a duty cycle of 10 to 90 %) to the fuel pump control units. These evaluate the PWM signal and actuate the fuel pumps with a PWM signal as required, so that the actual fuel pressure value corresponds to the specified value. Depending on the fuel requirement, fuel pressure is varied between 3.0 and 4.8 bar. The fuel pumps are actuated independently of each other.
Emergency running
- If the "fuel pump ON" ground signal fails or is implausible, the fuel pumps are shut off.
- If the "specified fuel pressure" signal fails or is implausible, the fuel pumps are shut off.
- If the "circuit 15" signal is missing or implausible, the fuel pump control units, and therefore the fuel pumps, are switched off.
Coding
Since the two fuel pump control units are identical in construction, they must be coded differently. For its coding, the RH fuel pump control unit is given a coding link between PIN 6 and PIN 7.
Tank-draining function
The fuel tank can be drained using the fuel pump control units 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
- Specified fuel pressure 4.8 bar
During draining, Xentry Diagnostics must remain connected and the ignition must remain switched on.
Diagnosis
The fuel pump control units carry out a self-test and a component test. Recognized errors are stored by the fuel pump control unit and sent to the Xentry diagnostics via the diagnostic CAN (CAN D) to the ME-SFI control unit over the drive train CAN (CAN C).
Variants
The vehicle and engine variants are already stored in the fuel pump control units. If a fuel pump control unit is replaced, it must be given the variant coding.
