It has been a long time since you asked this question, but.....My car has the 90 liter fuel tank (option code 915). 23.5 gal, and the reserve light comes on when there are 2.6 gal left. I re-read your post, and am surprised the dealer couldn't tell you what you had. Call a dealer, give them your VIN #, and they can tell you what recalls have been issued for your car, what repairs due to recall have been made, and what options your car came with.