The volume of the tank on your C4 is 17L.
When the remaining driving range is between 375 and 1500 miles, a UREA warning illuminates and a signal lights up every 200 miles. Between 0 and 375 miles, the warning light SERVICE illuminates and the indicator UREA flashes, along with an audible signal and the display of a message indicating the remaining mileage. The message is shown every 30 seconds if the level has not been adjusted. When the tank is empty, put a minimum of 3,8L in the tank to turn off the warning light
When your tank level reaches 0 miles, you will not be able to restart the engine once it has stopped. If your engine is still running, you can drive to a gas station. In case of a breakdown, wait for 5 minutes before adding AdBlue®. You need to turn the ignition on for about 15 seconds to then start the engine.
This information can vary on some vehicles of the same model in relation to the options chosen by the manufacturer.