# How is fuel consumption measured?



## Patman (May 7, 2011)

The accuracy is typically optimistic. Usually when I am looking at my DIC @ 35 - 37 actually it is more like 32 - 33MPG. It does get better over time once the computer learns how you drive, but still not perfect. IMO it is all based on RPMs/vs distance traveled. It will give you an idea of where you are. After I fill up sometimes I will take a back road to my house and I will get the MPG up to 70s - 90s. I am traveling all downhill tho and then once reality sets in(stopping and hills) I am back to the mid 30s in my Eco in the city. I am not sure how it is actually calculated but it gives you an idea and something to work on/for. Sorry I misread that I was thinking MPG calculations. Most people ask about that. Fuel is going to be the same. Gets more accurate with time.


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## AutumnCruzeRS (Sep 10, 2012)

I thought it was read on fuel level percentage from sending unit level.


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## KpaxFAQ (Sep 1, 2013)

For the diesel, it is very accurate. Not sure how it works but it's usually Optimistic!


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## Aussie (Sep 16, 2012)

Not sure about the DIC as I rely on KM's done compared to how much fuel I put in. I have noticed that when my trip meter which I zero each fillup reads distance done the same as distance to go the gauge is on half.


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## diesel (Jun 8, 2013)

I see a discrepancy during regens. If I am coasting during a regen, my instant MPG will be pegged at 99MPG but the average will drop.


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## CosmosGoat (Sep 23, 2013)

It may be calculating based on the injector pulse. The computer knows the flow of the injector given a fuel pressure and can calculate the amount is injects on each pulse. I have found the MPG on my TD is pretty darn close, within 5%, when compared to my fuelly calculation.


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## pL2014 (Dec 29, 2013)

I've been keeping track of mine using the odometer/pump and the DIC. I started keeping detailed track on my 2nd tank, so nearly the entire 6 months I've owned the car. My odometer/pump average is 28.3 (mostly city, very cold MI winter, mostly pre-break-in, but my last several tanks have all been in the 33-36 range). My DIC average is 29.2. Slightly optimistic. I've had individual tanks vary by as much as 3 mpg between the odometer/pump and the DIC. I've only had 1 tank so far where the DIC was lower than the actual.

As to how the computer measures fuel consumption, I'm not sure. I know you can install aftermarket meters that plug into the ODB-II port, so I'm assuming the engine fuel flow rate is measured/calculated someplace.


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## oilburner (Jun 13, 2013)

CosmosGoat said:


> It may be calculating based on the injector pulse. The computer knows the flow of the injector given a fuel pressure and can calculate the amount is injects on each pulse. I have found the MPG on my TD is pretty darn close, within 5%, when compared to my fuelly calculation.


correct, you win the prize. injector on time measured in milli seconds


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