Fuel indicator not changing after adding fuel

[Danks]

My wife and I test drove a Clarity today. I scheduled the test drive and the dealer - Fox Honda of Grand Rapids, MI put the car in the showroom and had it charged for me when I got there. The fuel indicator was 2 bars and the battery was 1/2 charged. (They turned the heat on the car before we got there.)

We were running on HV Charge on the freeway and the low fuel light went on - 53 mile range. We stopped and I added 1 gallon of gas. I was expecting that the fuel bars indicator would show the added fuel - it didn't - and that the range # would change - it didn't. Is this normal? Was there something I was supposed to do to get those to update? The low fuel indicator also stayed on.

We loved the car BTW.
Thanks,
Al

 

[Walt R]

I haven't had my Clarity long enough to confirm, but prior experience (and forums) with a Prius is that there is a minimum amount to add to have the fuel gauge increase - around 3 gallons.

I surmise that this is due to the digital fuel gauges and the complaints the manufacturers would get if bars winked on and off as the car went up and down hills, braked, etc. It would be more noticeable than a slight increase on an analog gauge.

 

[petteyg359]

We stopped and I added 1 gallon of gas. I was expecting that the fuel bars indicator would show the added fuel - it didn't - and that the range # would change - it didn't. Is this normal? Was there something I was supposed to do to get those to update?

Yes. Fill it up. First for the obvious reason that it doesn't track the tank level very well if you don't. Second for MPG tracking (because there has never been a car where the computer actually showed accurate MPG, and sometimes noticing MPG changes can alert you to problems that don't show other symptoms). You can't calculate it if you don't fill the tank, because until you actually fill it, you'll never know how many gallons you actually burned.

The car obviously has a sensor like every other vehicle to track the fuel level in the tank, but it doesn't actually measure flow (as in gallons). Not only does not properly filling up prevent you from measuring your mpg, but it also prevents the car from doing so. Especially when you only put in a tiny amount. See https://auto.howstuffworks.com/fuel-gauge1.htm, about float meters and that fuel tanks aren't simple rectangular boxes.

 

[KentuckyKen]

The Clarity seems to be notorious for slow gas gauge response. Mine doesn’t show the change after fueling until I drive some. First time I fueled up, I over filled the tank because the gauge didn’t respond and show a full tank after the nozzle clicked off. I learned my lesson and now don’t add any more gas when the nozzle shuts off. Well, I hope I remember since it’s been 7 months and counting since I last filled up.

 

[qtpie]

I had similar issue with my Toyota Venza in the past, so I think this is normal. It seems that if you add very little gas (~1.5 gallons in our case), then the digital gauge does not automatically reset.


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[Fast Eddie B]

The car obviously has a sensor like every other vehicle to track the fuel level in the tank, but it doesn't actually measure flow (as in gallons).

Are you certain?

My assumption is there must be a way it measures fuel flow. Maybe not linked to the fuel gauge in any way, but how else would the car display instantaneous fuel consumption? I guess there might be other ways to guess at it but a fuel flow sensor would be the most elegant way.

Anyone know for sure?

 

[MNSteve]

The car obviously has a sensor like every other vehicle to track the fuel level in the tank, but it doesn't actually measure flow (as in gallons).

My assumption is there must be a way it measures fuel flow.

I believe that the two of you are talking about different things here. Pettyg means "fuel flow" into the tank during fillup. Eddie means flow from the tank to the engine while driving. I think you're both probably right. I don't know how the car measures incoming fuel added to the tank but it seems obvious that adding a gallon or so causes the gauge to be wrong, at least initially. And there must be some measure of outflow to generate the instantaneous mileage indication.

 

[LegoZ]

As the ECU knows Fuel pressure, injector size and injector pulse width it can calculate the fuel economy of the car both instant and over a longer term with some amount of accuracy.