Fuel supply, function

Function requirements for ignition OFF, general points

 Circuit 87M (engine timing ON)

 Terminal 15

Ignition OFF, general points

With ignition OFF, first the engine and then the engine timing are switched off in the CDI control unit (N3/9).

Function sequence for ignition OFF

For ignition OFF the electronic ignition lock control unit (N73) switches off the engine compartment circuit 15 relay (K40/8kJ) via the interior CAN (CAN B).

If the CDI control unit receives the "Circuit 15 OFF" signal over the engine compartment circuit 15 relay, the following components will be switched off and the processor power-down is started:

– the fuel pump (M3) from FSCU (N118)

– pressure regulating valve (Y74)

– fuel injectors (Y76)

– quantity control valve (Y94)



After stopping the engine (after ignition OFF) the AdBlue fluid is suctioned back out of the AdBlue® metering valve (Y129) and the AdBlue metering line in the direction of the AdBlue tank through the AdBlue® extraction pump (A103/2m2). The AdBlue metering line is only partially emptied in the process. The AdBlue® metering valve is opened during the suctioning back process so that no vacuum arises in the AdBlue® pressure line. Since after stopping/parking the vehicle it is not possible to exclude the possibility that the outside temperatures drop into negative territory (for very long stopping/parking), the suctioning back of the AdBlue fluid out of the metering valve and the AdBlue line takes place after every switching off of the ignition

The processor run-on period for the AdBlue® control unit (N118/5) is determined by the CDI control unit and lasts about 4 s. It can, however, last for several minutes due to various functions (such as On-board Diagnosis (OBD), Drive Authorization System (DAS), thermal management.

When computer run-on is complete, the circuit relay 87M (K40/8kN) is switched off and the engine timing system is disconnected from the on-board electrical system (switched off).



System tests are conducted by the CDI control unit during the processor run-on period and the fault memory is updated.

The "circuit 31" ground connection is made from the on-board electrical system battery (G1) via the battery ground point (W10) and multiple ground lines to the right front assembly compartment ground point (for lamp unit) (W2).

When the ignition is OFF, the CDI control unit is supplied with power from the on-board electrical system battery via "circuit 30 fused".

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Function sequence for fuel system high-pressure circuit

The high-pressure circuit consists of the following components:

– fuel system high pressure pump

- left rail

- right rail

- high-pressure line

- high pressure fuel pressure sensor

– fuel temperature sensor

– pressure regulating valve

– fuel injectors

dependent on the signal received from the accelerator pedal sensor (B37), the engine speed and the fuel temperature, the fuel system high pressure pump delivers fuel to the left rail and from there simultaneously to the right rail.

The fuel passes from the respective rail via the high-pressure lines to the fuel injectors. The fuel injectors spray fuel in a fine atomized form. The CDI control unit calculates the injection quantity selectively for each cylinder based on a characteristics map for the respective operating condition. The injection quantity is dependent upon the fuel pressure in the rail and the actuation duration of fuel injectors.

The fuel pressure in the rail is controlled by the pressure regulating valve and quantity control valve. The actual applied fuel pressure in the rail is detected by the high pressure fuel pressure sensor and is limited by the pressure regulating valve to a maximum of 1800 bar. The fuel temperature is detected over the fuel temperature sensor. Both pieces of information are passed on permanently to the CDI control unit.

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Function sequence for safety fuel shutoff

The safety fuel shutoff system is designed to ensure traffic and passenger safety.

The CDI control unit controls the safety fuel shutoff on the basis of the following sensors and signals:

- crankshaft Hall sensor (B70), engine speed

– supplemental restraint system control unit (N2/10), direct crash signal

– Supplemental Restraint System control unit, indirect crash signal over the user interfaces-CAN (CAN-HMI), the electronic ignition lock control unit, the suspension FlexRay (Flex E), the powertrain control unit (N127) and the engine CAN (CAN C)

The safety fuel shutoff is activated by the CDI control unit in the following conditions:

 Absence of the engine speed signal

 Crash signal

Absence of the engine speed signal

If the engine speed signal generated by the CDI control unit is missing the fuel pump will be switched off.

Crash signal

If the CDI control unit receives a crash signal indirectly or directly from the Supplemental Restraint System control unit, it switches off the fuel pump, the quantity control valve and the pressure regulating valve and shortly actuates the fuel injectors to make the fuel system unpressurized.