We continued to drive it for well over a thousand miles before I finally tackled it. I was armed with a Eolys refill kit and 1 litre of Eolys 176 (green).
You read posts that suggest that the Eolys additive is not being added as soon as this low level is reached. I can say and have taken photographic proof.
Firstly I tried to refill the Eolys Tank by removing the overflow/refill plug and refilling the tank with a 1 litre bottle with a clear tube attached.
The plug unscrews by hand and note the green label on it that signifies Eolys 176. Here is a picture
I only managed to get less than 200ml before it started to overflow. ????? I thought. So replaced the filler cap and got out my Lexia 3.
Here is proof that the car had regenerated during the previous 500km. Not proof that the Eolys was being added but the car was regenerated still and there was no FAP fault.
The Lexia 3 identified the low level of Eolys fault as P1446 Fuel additive low level reached.
There is no way that the ECU can identify the actual level. The warning is based on mileage. The previous image says at the bottom line " Distance Level Reached?" "yes".
With the car Eolys filled to the brim the car still had the annoying low level reached message.
How much Eolys_176 do our cars use? The Lexia 3 gives you the figures
Eolys_176 30,000 miles should be 42g. Just 42g. So a litre should be good for 714,285.7 miles!
I read somewhere that the car has enough Eolys_176 for the vehicles lifetime. If the tank contains 3 litres this would equate to over 2 million miles of motoring. The most miles I have achieved from a C5 was 276k when I scrapped the vehicle due to clutch failure.
So it rather looks like we are wasting our time trying to refill these tanks. So how do we reset by the Lexia 3?
Just to show what ECU our C5 has EDC15C2
It says our car has only 105 grammes of additive remaining. ECU fault code P1446.
The Lexia 3 lied about the engine speed. 
These series of photos show the navigation of the system.
This says replace the additive ECU. I did not. Our RPO number is 09713 which indicates Eolys_176
At this point I have to say that I did not take these photos before I managed the reset so the next photo shows 2,111g added to the system. this was after I had reset it. But you can see the figure is in yellow that allows you to change the figure. This was 0000000 previously.
Notice that it states that 0107.850g of additive had been used since the last time the tank was filled.
Changes the amount of additive added figure. This effectively resets the ECU.My Lexia 3 was bought on a well known online shop from a company called tools4car. The cost was 109.99p in November 2015. They are now £115. Installation of the software requires patience and no internet connection! (The internet connection must be switched off)
Here is the link
http://www.ebay.co.uk/itm/FULL-CHIP-REV ... SwknJX1zDK
Now I have provided you a step by step with photos of the resetting of the low additive warning level it makes me want to ask the question
"Why does the warning level come up after less than 100k?"
Was it a fault at the factory or the PDI? Or has it been as a result of the actions of a rogue? It seems to affect a lot of cars.
I am pleased that I can reset this myself and if anyone lives within driving distance of Maidstone, Kent I should be able to help if they private message me.
I trust this helps.
I believe that this will still apply to all the C5s. My lexia3 shows the Mk2 and the Mk3 models.
