Let’s start with the concept of a dealership charging for a problem that is probably a warranty claim in the first place. Warranty repairs shouldn’t cost the owner anything, so the dealership is skating on thin ice in the first place.

But secondly, this doesn’t sound like a problem at all. In fact, I’d say it’s perfectly normal behaviour. What’s happening is that the car’s computer is looking at how much fuel the vehicle has used in the immediate past, and calculating how far you can go on the fuel you have left, at that rate of consumption. When you switch from stop-start running to highway driving, your consumption per 100km falls. When the computer notices this, it recalculates how far you can go with your reduced consumption, and the estimated range on the trip-computer goes up.

Fuel range is the inverse of fuel consumption, when consumption goes down, range goes up. And since the car’s computer models the range based on your recent consumption rate, highway running will usually cause the range to creep up. Eventually the range will plateau and then begin to fall. When you hit the city, the range will begin to fall more quickly. The dealership should have been able to explain this to you rather than threatening to charge for taking a look at it.