Holden says they can re calibrate the gauge but will take 2 hrs and cost $150, don't want to spend that money if it doesn't do anything.
When your gauge shows you have 1/2 tank when you enter the menu through mode/set before turning the key to ign, and scroll thru what value does it show ?, should show you litres remaining etc. Write it down for your record to show them eg what it reads at full,3/4,1/2,1/4 and empty, (why empty ) because you stated you could only fit 50lt in.
By the way Holden recalibrated my VY ute fuel gauge via OBD port using their Tech 11,as well as uploaded latest software in relation to fuel gauge, took all of 15mins and I was with them in the car the whole time, its bloody amazing what can be optioned to become active, total cost $20
2hrs sounds about right though, unless you know the boys behind the service desk, then it becomes abit more flexible eg; When your car comes out from being serviced, they,ll wander out to where its parked and meet you there and plug and play.
But as they told me its amazing how many people have a problem and the first thing the customer wants is a price on a new sender, when all it needs is recalibrating and the latest software uploaded,if you purchased the sender off a Holden dealer go back to them and ask if you come back when its quiet can they pop out and plug the Tech11 in and see if the new sender is o.k or if its the gauge that needs recalibrating,,, just trying to help ya out CAM, and save ya a few bucks mate,
Cheers CONROD