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

Functional description

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.

Item Explanation Item Explanation
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.

Item Explanation Item Explanation
1 Electronic fuel pump with direct current motor

Pin assignments

Pin Explanation
SIG Minus line
U Supply voltage
4 pins not used.

The following graphic shows the electronic fuel pump with 3-phase motor.

Item Explanation Item Explanation
1 Electronic fuel pump with 3-phase motor

Pin assignments

Pin Explanation
SIG Minus line
U Supply voltage, phase 1
U2 Supply voltage, phase 2
U3 Supply voltage, phase 3

Nominal values

Observe the following nominal values for the electronic fuel pump:
Variable Value
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

Diagnosis instructions

Failure of the component

If 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.

 

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