I tend to treat the Adblue system on my vehicle much like the windscreen washer fluid - I top it up every month. My own theory behind this is that by keeping the tank topped up, there is less air in the Adblue tank which reduces the risk of rust to any remaining metallic components in the tank (despite later tanks having been redesigned with more plastic parts to help prevent this) and also prevents any crystallisation of the Adblue on components when the tank gets low on Urea.
If the Adblue level alert is going haywire, that would indicate that the fluid was well low and may be causing the erratic readings. However if you have filled the system as per the manual
Time will tell no doubt, but with the cost of these tanks such as they are, it doesn't cost me anything more that time as part of regular checks to do.
I hope your dealer will resolve this for you. They may charge for the diagnostic, but that will be a relatively smaller price to pay if they resolve the issue for you. Don't forget if you have any hassle, as long as the car has been regularly serviced according to the manufacturer standards and at the required intervals, they should cover this for you. If you have any hassle, don't hesitate to contact Citroen Head Office and complain directly. They will ask if you have been to the dealer - which is where they will then contact them directly if the dealer is not playing ball.
Good luck, keep us posted.
Just one other point, my vehicle has a specific warning regarding topping up of Adblue when it has run out - so there are specific actions to and not to take:
Important: in the event of a top-up after a breakdown because of a lack of AdBlue, it is essential to wait around 5 minutes before switching on the ignition, without opening the driver’s door,
unlocking the vehicle, introducing the key into the ignition switch, or introducing the key of the “Keyless Entry and Starting” system into the passenger compartment.
Switch on the ignition, then wait for 10 seconds before starting the engine.
