Electric fuel pump
The electronic fuel pump is an in-tank pump and it supplies the engine with fuel (diesel fuel or petrol).
The electric fuel pump is activated via either an electronic fuel pump control module (EKPS) or a fuel pump relay.
If the vehicle is fitted with the electronic fuel pump control system, the electric fuel pump is activated in line with requirements. The engine control unit (DME or DDE) calculates the required fuel quantity based on the driver's choice and the operating condition of the engine at that particular time. The required fuel quantity is transmitted to the electronic fuel pump control module (EKPS) in the form of a message on the CAN bus.
This message is converted into a pulse-width-modulated output signal by the fuel pump control module (EKPS). For this purpose, the characteristic curves for the fuel requirements are stored in the fuel pump control module (EKPS). The characteristic curves are coded for the specific motor and model.
If the electric fuel pump is activated via the fuel pump relay, the engine control unit (DME or DDE or RDME) switches the electric fuel pump on or off. The fuel pressure in the feed line is approx. 5 bar and is regulated at this level by a pressure limiting valve inside the electric fuel pump.
DME: Digital Motor Electronics
DDE: Digital diesel electronics
RDME: Range extender digital engine electronics
When controlled by the fuel pump relay:
The fuel pump relay is activated via the engine control unit (DME or DDE or RDME) and closes a circuit. In the closed circuit, the power distribution box, engine control unit and electric fuel pump are interconnected. This switches terminal 30 (power supply) to the electric fuel pump.
When controlled by the electronic fuel pump control module (EKPS):
The fuel pump control module (EKPS) uses a pulse width modulated output voltage (PWM signal) to regulate the speed of the electric fuel pump, thereby ensuring that the electric fuel pump delivers precisely the amount of fuel required.
With the direct current variant, the fuel pump is driven by a DC motor with permanent magnet.
With the rotary current variant, the fuel pump is driven by a brushless three-phase motor with permanent magnet.
Compared to the direct current motor, the 3-phase motor delivers higher output power.
|1||Service cap (with connections for components inside the fuel tank)||2||Plug connection for the electronic fuel pump|
|3||Plug connection for the fuel level sensors||4||Float on lever arm fuel level sensor 2|
|5||Electric fuel pump|
Structure and inner electrical connection
The electric fuel pump is connected to the EKPS control unit or fuel pump relay - and therefore the engine control unit (DME or DDE or RDME) - via a six-pin plug connection.
The following graphic shows the electronic fuel pump with direct current motor.
|1||Electronic fuel pump with direct current motor|
|4 pins not used.|
The following graphic shows the electronic fuel pump with 3-phase motor.
|1||Electronic fuel pump with 3-phase motor|
|U||Supply voltage, phase 1|
|U2||Supply voltage, phase 2|
|U3||Supply voltage, phase 3|
Nominal valuesObserve the following nominal values for the electronic fuel pump:
|Voltage range||6 to 16 V|
|Nominal voltage||12 ± 0.1 V|
|Operating pressure when driving with petrol||5.2 to 5.9 bar|
|Operating pressure when driving with diesel fuel||3.6 to 5.9 bar|
|Pressure limiting valve when driving with petrol||7.0 to 10.0 bar|
|Pressure limiting valve when driving with diesel fuel||6.2 to 7.0 bar|
|Temperature range||-40 to 85 °C|
Failure of the componentIf the electronic fuel pump fails, the following behaviour is to be expected:
- Fault code entry in EKPS control unit or engine control unit (DME or DDE or RDME)
- The warning and indicator light lights up in the instrument panel
- Check Control message in the instrument panel
Function check of the component
A function check of the electronic fuel pump can be performed using the diagnosis system.