Electronic fuel pump control module (EKPS)
There are two control unit versions for the fuel pump control module. The control unit version depends on the design of the fuel pump. The electric fuel pump is either activated as a direct current motor with permanent magnet or brushless three-phase motor with permanent magnet.
With a three-phase motor, multiple drivers are required in the EKPS control unit, but only one driver for a direct current motor. By changing the coding, e.g. characteristic curves, type of control or diagnosis, it is possible to operate different DC or EC versions of the fuel pump with a control unit version.
The EKPS control unit is connected via PT-CAN or PT-CAN2 (depending on the series).
The engine control unit calculates the required fuel quantity based on the driver's choice and the operating condition of the motor at that particular time. The required total quantity is sent as a message to the control unit of the electronic fuel pump control module (EKPS) via the bus. This message is converted by the control unit into a pulse-width modulated output voltage. For this purpose, the characteristic curves for the fuel requirements are stored in the control unit. The characteristic curves are coded for the specific motor and model.
There are 2 types of controls:
Speed control (load)
The control unit controls the speed of the electric fuel pump with a pulse-width-modulated output voltage (PWM signal). In this way the delivery is precisely matched to the requirements.
The actual speed of the electric fuel pump is evaluated as follows: The current flow at the fuel pump exhibits a certain ripple. The ripple corresponds to the number of segments of the commutator (= the number of armature windings of the electric motor). Per rotation, the number of current pulses is equal to the number of segments. This value is used to calculate the actual speed of the fuel pump.
The motor control evaluates the pressure in the fuel feed to the motor via a fuel low-pressure sensor. By means of a nominal/actual value comparison of the pressure, the motor control system sends a request signal to the control unit of the electronic fuel pump control module that corresponds to a certain voltage for the electric fuel pump. The control unit of the electronic fuel pump control module controls the output voltage for the fuel pump by changing the pulse width modulation depending on the existing vehicle voltage. This ensures that the fuel pump power needed to develop the fuel pressure is only as large as necessary for the low pressure fuel system.
|1||Control unit of the electronic fuel pump control module (EKPS)||2||Plug connection 16-pin, connection to the wiring harness|
|3||Plug connection 4-pin, connection to the electric fuel pump|
Structure and inner electrical connection
The control unit of the electronic fuel pump control module has two plug connections: one for connecting the main wiring harness (large connector) and one for connecting the electric fuel pump (small connector).
To avoid installation of the wrong control unit version, the small connectors are differently coded. The coding of the connector and socket on the control unit is also identified by different colours. The large connectors all have the same coding.
The control unit is a bus user on the PT-CAN or PT-CAN2. The EKPS control unit is supplied with terminal 30B via the rear power distribution box.
The control unit is woke up by the Car Access System (CAS) or front electronic module (FEM) via wake-up line (terminal 15 wake-up line).
For overheat protection, temperature sensors (the number depends on the control unit version) are placed in the immediate vicinity of the power semiconductor.
|1||Control unit of the electronic fuel pump control module (EKPS)|
The graphic above shows only the supply and bus connection. The current pin assignment is located in the wiring diagrams in the ISTA diagnosis system. Click on the component code in the wiring diagram to activate the "Installation location" and "Pin assignment" tabs.
Nominal valuesPlease note the following nominal values for the control unit of the electronic fuel pump control module (EKPS):
|Supply voltage||6 to 16 volts|
|Nominal current||100 mA|
|Maximum actuation of the electric fuel pump||18 A|
|Frequency of the pulse-width modulated signal (PWM signal)||20 kHz|
|Temperature range||-40 to 80 deg C|
Failure of the component
If communication to the control unit of the electronic fuel pump control module (EKPS) fails, perform the standard checks (global testing procedure). If there is an internal control unit fault, the following behaviour is to be expected:
- Fault entry in the control unit of the electronic fuel pump control module (EKPS).
If communication with the motor control unit is missing or faulty, the control switches the electronic fuel pump control module to emergency operation. The electric fuel pump is fully activated.