And there we have it, people claiming its 'easy' to get over 600km. I doubt you are driving till you run out of fuel on the side of the road either. So assuming lying isn't the issue, there must be something wrong with my economy because its nowhere near 'easy' for me to get anywhere close to 600km. Yes I drive it hard and fast but if it were 'easy' to get 600km then when I drive it like a granny I should 'easily' see 650-700km, not barely scraping 550

So worth replacing the o2 sensor? anything else that might be an issue?
Would even disconnecting the battery to reset everything help?