How do fuel gagues work and how much to fix them?

[Vanilla]

I have a 306 HDi. I had my low pressure fuel pump replaces two weeks back at the dealership.

Now my guage is not working correctly. On a full tank where i've only done 100 miles it's showing as almost empty (hope it's broken or i've just leaked £40 worth of diesel!).

It also acts erratically now and again. Hopefully the garage will admit it was something not done correctly when they changed the low pressure fuel gague (or are they not connected?).

So how much are they to fix? expensive? time consuming?

Thanks for any advice.

 

[Vanilla]

Hmm interesting, the rear seat bench is where the low pressure fuel pump is - which they changed two weeks ago. I'm hoping they damaged it when they changed it and I don't have to pay tons to get it fixed.

Thanks for the info