How accurate are the factory installed MPG computers

Rkh · Mar 1, 2014

How accurate are the factory installed MPG computers that are installed on new vehicles? I have a 2013 Avalanche, took a trip & computer said 18mpg-but I figured 13mpg using the old method of gallons of gas used divided by miles traveled(I zereoed the computer on avalanche).I had the vehicle for a year and have different readings then what the computer says on other trips. you wonder if they do this on purpose to make it look like vehicle is getting better mileage then reality.

John M · Mar 1, 2014

The one in my 1500 is a joke. My 08 Duramax was getting 15 - 18 depending on the time of year. Took it on a trip to Florida was getting 22 on the highway by the computer, 20 by pencil. This 1500 got like 16 on a day trip out of town, averages 13 by pencil daily. I hate this 6 speed transmission on this thing. Cant use the cruise on the highway without it downshifting on every little incline. One of the guys at work has a 2014, says his does the same thing. Probably the last Chevrolet truck Ill buy.

Anonymous-0 · Mar 1, 2014

I had a Ford that was right on the money. It was off very little, the times I checked.

dhamps10 · Mar 1, 2014

When I got my 13 Silverado, I checked it several times, and the computer was RIGHT on. Maybe I have 1 a million ?

IHRedRules · Mar 1, 2014

When I had an 08 silverado, I let it go without resetting for about 3 1/2 years, or so and it said 16.7 mpgs when I traded it in, the hand calculated avg over that time was 16.7. I felt it was storing and using a lot of data, as it was hard to get the avg to change. I now have a Ram and the avg is forever changing, drive 10 miles and you could go up or down several tenhts. I think the ram only tracks the last few miles, relatively speaking, to calculate its avg. it's also about 1-1.5 mpgs high.

26cows · Mar 1, 2014

They are not that accurate. Short term ok, long term not. When you do the math you have to be accurate with how much fuel you start with and how much you refill. If the level is not the same the numbers will be off. Depending on your gear ratio and engine size you should get 15 to 20 mpg. It also depends on your driving. Stop and go. David

just another old geezer · Mar 1, 2014

Have them on both 05 jeep liberty diesel and 09 dodge 2500 6.7 cummins. Computer runs constantly
2 mpg under actual milage.

Russ from MN · Mar 1, 2014

Ours are fairly accurate, car used to be under 5-10% but this winter it was almost right on, and disappointing! And I agree with John, I don't like the GM 6 speed. If you don't trust it, check it with a calculator, and fuel up consistently every time.

Two Dogs · Mar 1, 2014

I've checked by pencil the one on my Government Motors Impala and it is very (sub 1 mpg) close. TDF

jm. · Mar 1, 2014

2012 ford f 150 over 55,000 miles and the computer is right on the money overall. We record ever gallon of gas that goes in the vehicle.

GordoSD · Mar 1, 2014

Any reason not to drive in 5th? Probably get better mileage than "lugging" your engine in 6th?

Anonymous-0 · Mar 1, 2014

96 grand Cherokee--right on the money

Anonymous-0 · Mar 1, 2014

My 13 Honda accord seems very close to accurate? Used to have a Buick Lasabre which was 10 Percent high.

Dean · Mar 1, 2014

It's an automatic. The electronics control shifting.

Do you want to continually shift between D and M in order to force 5th?

Dean

pete black · Mar 1, 2014

08 gmc was quite accurate. agree with others gm 6 speed in a 2010 sucked to the point i traded it off.

onefarmer · Mar 1, 2014

2004 Taurus is quite accurate.

I do think they are closer with full tank refills(10-15+gals) rather than 0-5gal top offs.

JRSutton · Mar 1, 2014

I'll second the 96 grand cherokee - can't argue with mine.

old bc · Mar 1, 2014

My 2011 Impala is very accurate.

Bob · Mar 2, 2014

The vehicle 'puters have NO direct way of knowing the gallons used/temp/specific gravity of the fuel.

There's NO physical flowmeter/MPG meter.

The 'puter ASSUMES the factory flowrate of the injectors, and then factors in the injector duty cycle, and engine speed and comes of with a number that will be accepted by/make the average owner happy.

Some years back some "chip" manufacturers got in trouble 'cuz their software made itself look better/better by reporting better/false MPG with NO improvement at gas pump.

Then, one or two mfg's got in trouble for "tweaking" the odometer readings by a few % high to make their apparent mileage slightly higher.

Bottom line is that the indicared MFG's have NO incentive to make the reading accurate or honest.;

GVSII · Mar 2, 2014

Wifes '11 escape,bought new,and for the first few thousand miles the read out was high,anywhere from 1 to 2 MPG high.After some miles built up and 3 years it's never more than .5 MPG off.

MarkB_MI · Mar 2, 2014

Over one tank of gas, it's very unlikely your calculation will be more accurate than the computer. Try averaging over ten tanks.

Blackhole49 · Mar 2, 2014

In my opinion, the only way to compare is over a long period. I drove an Audi TT from CA to MI last summer, 3,400 miles. 2,000 on non highway roads with the majority in the mountains, the rest on expressway. Even though the computer reset after 2,000 miles, it consistently said 32mpg average. Total trip and total gallons worked out to 31.89mpg. Made a believer out of me.

How accurate are the factory installed MPG computers

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