Trip computer miles to next refuel counting up

[Fragmeister]

I've just bought a second-hand Grand C-Max 1.6 TDCI Zetec 15 plate (May), 15k miles, that was previously a rental car.  In the week I've had it, the trip computer screen that counts the miles down until the fuel tank is empty, isn't behaving as expected.  When I got the car, it read 77 miles and when I put fuel in, it read 490 miles but counted upwards and ended at over 600 miles when I put 37 litres of diesel in to fill it.

 

After filling, the computer read 660 miles and for three days counted down as far as 542 miles but this afternoon counted back up to 565 miles.  Now I know this isn't normal but does anyone think it is electrical or mechanical, easily fixed or a big job. The car is still under warranty.  Any thoughts?

[TomsFocus]

Sounds normal to me, the older ones can only go down so can stick on one number for a while, but if you're driving more economically I don't see why the miles shouldn't go up.

[iantt]

Quite normal for this to happen, depending on the fuel econnomy on each drive cycle.

[Philf1]

My mate got his Audi from 660 miles to nearly 800 to empty and had driven from Yorkshire to silverstone

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