I recently started the car knowing that i had run the car down to nearly the fuel light was about to go on But on starting the car up it suddenly showed Half a tank and the obc says it has 300 odd miles before empty rather thsn the 70miles it showed previous!
I put £25 of diesel in today thinking this might reset the guage but this has now moved the guage further to full!
Is there a way of resetting or calibrating the guage/ sender as i know there is considerably less fuel in the tank than what it is now showing and don't want to run out of diesel
Sometimes the float sticks, then frees itself again. It's happened to me once or twice, then worked normally for prolonged periods. I would just mentally calculate how many miles you have left, (with a margin for safety), then fill it again. It may well sort itself out.
I would avoid trying to remove the sender unit / lift pump for as long as you can - it can be a serious PITA to remove and refit.
2002 HDi 2.2 Exec Estate, (2008-12) (wonderful)
2003 HDi 2.2 6-speed Exec Estate (2012-19) (also a gem)
2009 Citroen C5 2.0 HDi VTR+ Estate (godawful heap)
2008 BMW E91 330i touring (great fun - murdered by a reversing SUV)
2007 BMW E91 325i touring (slower smoother quieter)
This happened once on my old 406, now it happens on a regular basis on my new 406...
I always reset the trip computer/ dashboard miles when I fill up, so imagine my surprise the gauge was dropping quicker than usual and when I only covered 350 miles before the light came on. I just assumed it was lots of stop/start journeys and didn't think about it too much but when I started the car to go to the fuel station I magically had half a tank and 300 miles left. I didn't really trust the gauge but I only* got another £45 in the tank - its like a gift really....
It now does this every time, but I'm not bothered about fixing it as I use the trip computer and if it gets low faster than I though I just play it safe and bung some diesel in.
I think its to do with the lack of use, as I only use my car maybe once in every 10 days - which is a shame - but its bought and paid for and doesn't owe me a lot so its useful to have, plus it puts a smile on my face when I drive with 'passion'
2003 2.2hdi estate - mine 1998 Volvo 940 auto estate - also mine 2019 Citroen C3 something - the wife's PP2000 user, can help with faults / diagnostics in the Bournemouth area.
Mine does this all the time & has as long as I've had it
You get used to it I've done 25k in mine now using it every day & I just live with it.
If I brim it I get about 750 miles maybe a bit more depending on how I drive
But it will show nearly empty by 450miles on the trip & then the next morning the range will say 350ish & the fuel gauge will have jumped up to over half full
Just live with it & learn to gauge how many miles you have done (trip) by how much you have put in
Hope this is of some help DDD.
2002 110 HDi estate, Rapier in monaco blue! ( found quite a bit more power ) SOLD I've sorted the airbag light
1998 3.0 V6 SE coupe in Diablo Red ( my baby ) sold
2006 206 1.4 16v sport in Aegean blue ( wife's shopping trolley )
2003 2.2hdi estate - mine 1998 Volvo 940 auto estate - also mine 2019 Citroen C3 something - the wife's PP2000 user, can help with faults / diagnostics in the Bournemouth area.
) SOLD I've sorted the airbag light 
run's for cover 