Digital Fuel level indicator faulty

[Frodoisdead]

Hi, got C5 2.0 diesel mk2 (2006) and digital fuel level indicator is playing. Not analogue but the one on the digital screen. It shows jumping mpg from 15 to 999mpg and keep changing. Also how many miles left of fuel in the tank, always jumping from one number to another. I remember had same problem when i had Picasso c4 (2008). How can this be fixed, is it some sort of sensor that needs replacing? Mamy thanks

[MikeT]

It's not faulty, it's how the Trip Meter works. Check your handbook or experiment by pushing the end stalk button on the right. It cycles between three displays. The first is live readout, the other two are accumulators.

[Frodoisdead]

It was working fine on picasso until one day and started flicking like that with mpg changing every second! I don’t believe it should work like that

[MikeT]

Are you saying it doesn't follow your right foot, which is how it should work?

[Paul-R]

First of all it's not a digital indicator of fuel level, it's an indicator of fuel consumption. As others have said it shows one of three mpg states. Two of them are based on an average over the distance as recorded by the two trip measurements and the third is a slightly smoothed instantaneous mpg readout.

It shows jumping mpg from 15 to 999mpg and keep changing.

That is exactly as it should be. It allows you to see the effect of backing off your right foot (!) and how hanging on to a high gear can sometimes be worse than allowing more revs in a lower gear.

Also how many miles left of fuel in the tank, always jumping from one number to another.

Now that shouldn't be changing rapidly at all except, possibly, just after you've filled up with fuel. I would expect it to change slowly as it counts down the amount of fuel left in the tank. If it is rapidly changing then that's not right. In fact I've not heard of that happening before.

[Gibbo2286]

Mine does the same, it is giving the actual instant fuel use depending on road and load conditions, downhill with engine braking it will show up to 999mpg because it's not using any fuel, up hill under load it can be down to 15mpg.

The distance to the need to top up works similarly, if you're cruising steadily it might estimate that you can go 60 miles, if you drive hard that estimate will come down accordingly.

The actual average mpg shown over the whole period on mine is around 39mpg, most of my travel is local pottering about with only a long distance trip monthly.