I put some petrol in the car today , not much about 10 litres.

It didn't seem to register on the gauge, that's a bargraph with limited
resolution but even so that was strange. Stranger still was that the
'miles to go' figure didn't change either, it stayed on about 90 miles.

I've never seen that before but I usually put more in, albeit
infrequently, it's not used much. The only difference today was that I
parked at the pump on the 'wrong' side because the garage was busy, and
wasn't close enough to get the nozzle in fully and it was upside down.
The petrol did go in the car and not on my feet.

I had assumed that the fuel gauge was a float on an arm jobbie, but
maybe it's more complicated. Any ideas?

It's an 04 Citroen Xsara Picasso.

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Cheers
Clive