In the Euro 6 diesel Tourans from 2016 two parts of the SCR (AdBlue) system typically fail: the tank level sensor (when the dash reads 0.0 mm or an empty tank with a full tank), and the tank heater, which gives up in winter. Both lead to the same place: the car starts a countdown, and at the end of the countdown it will not start. This is not a fault you can postpone, because the system shuts down under legal compulsion, and the tank is replaced from under the floor.

The drains inside the doors block up, and the water leaves not outwards but through the sill into the footwell. It goes unnoticed for a long time, because it collects in the foam under the carpet. By the time it gives off a smell, the connectors running in the floor are already corroding. Most of the electronics are under the third row, so look at the carpet there.