SCR System Modes: AFTERRUN

The system is shut down in AFTERRUN mode. If terminal 15 is switched on again before afterrun has been completed, afterrun is cancelled and STANDBY mode is assumed. If this is not the case the system goes through the submodes of AFTERRUN.

• TEMPWAIT (catalytic converter cooling phase) 

  In AFTERRUN mode, TEMPWAIT submode is initially assumed if the system is filled. This is intended to prevent excessively hot exhaust gasses being drawn into the SCR system.

  The duration of the cooling phase is determined by the exhaust gas temperature. EMPTYING submode is assumed after this time, in which the exhaust system cools down, has elapsed. EMPTYING submode is also assumed if a fault occurs in the system. If terminal 15 is switched on in this status, STANDBY mode is assumed.

• EMPTYING 

  The system assumes AFTERRUN_EMPTYING submode after the cooling phase. The pressure line and the delivery module are emptied in this submode. The urea-water solution is drawn back into the active reservoir by opening the reversing valve, actuating the pump and opening the metering valve.

  This is intended to prevent the urea-water solution freezing in the metering line or the metering module. The level in the metering line is calculated in this mode.

  PRESSURE COMPENSATION mode is assumed if the metering line is empty. PRESSURE COMPENSATION mode is also assumed if a fault occurs in the system. If terminal 15 is switched on, STANDBY mode is assumed.

• PRESSURE COMPENSATION 

  (intake line - ambient pressure) 

  After the system has been completely emptied, PRESSURE COMPENSATION submode is assumed. In this status the pump is switched off, the reversing valve is then closed followed by the metering valve after a delay. The time interval between switching off the pump and closing the valve prevents a vacuum forming in the intake line; pressure compensation between the intake line and ambient pressure takes place.

  After executing the steps correctly the system assumes WAITING_ FOR_SHUTOFF submode. WAITING_FOR_SHUTOFF is also assumed if a fault occurs in the system. If terminal 15 is switched on, STANDBY mode is assumed.

• WAITING_FOR_SHUTOFF  (shutting down SCR)

  The control unit is shut down and switched off.