Refer to Reducing Agent, Automatic Regeneration

WARNING: This page is about a different car, the 2015 Volkswagen Beetle. However, it is still accessible from the selected car via links, so may be relevant.

The reducing agent flows back into the reducing agent tank via the metering line to the Reducing Agent Injector -N474- after switching off the ignition.
Before working in this area, wait 10 minutes after switching off the ignition so that the recirculation can complete.
Likewise, wait 10 minutes after switching off the ignition before disconnecting the battery so that the recirculation process can complete, refer to [For transmission(s) 0A4, 02E, 09G, 02Q] Battery, Starter, Generator, Cruise Control .