Function requirements for ignition OFF, general points
Circuit 87M (engine management ON)
Terminal 15
Ignition OFF, general points
With ignition OFF, first the engine and then the engine management are switched off in the CDI control unit (N3/9).
Function sequence for ignition OFF
With ignition OFF, the electronic ignition lock control unit (N73) switches off the engine compartment circuit 15 relay (K40/8kG) via interior CAN (CAN B) and the front SAM control unit (N10/6) switches off the engine compartment circuit 15 relay.
The "Circuit 15 OFF" signal is sent redundantly by the electronic ignition lock control unit via chassis FlexRay (Flex E) to the powertrain control unit (N127) and via drive train CAN (CAN C1) to the CDI control unit.
If the CDI control unit receives the "Circuit 15 OFF" signal over circuit 15 engine compartment relay, the following components will be switched off and the processor power-down is started:
The fuel pump (M3) via drive train CAN and fuel system control unit (N118)
Fuel injectors (Y76)
Quantity control valve (Y94)
During the control unit run-on of the AdBlue® control unit (N118/5), the remaining AdBlue® reduction agent is sucked in by the AdBlue® extraction pump (A103/2m2) from the AdBlue® pressure line. The AdBlue® metering valve (Y129) is opened at the same time so that no vacuum arises in the AdBlue® pressure line. The duration of the run-on and the timing of the reduction agent return are dependent on the exhaust temperature as detected by the temperature sensor upstream of the SCR catalytic converter (B16/15) since excessively hot exhaust can damage the AdBlue® pressure line and other system components.
The processor run-on period is determined by the CDI control unit via drive train sensor CAN (CAN I) and lasts about 4 s. It can, however, last for several minutes due to various functions (such as European 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 management 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 at the front right (W10) and multiple ground lines to the right 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".
Referenced documents
- gf0716p9997orb Overview of system components for common rail diesel injection (CDI)