: MPG Computer Accuracy



JFJr
04-29-11, 01:33 PM
Has anyone checked the accuracy of the mpg computer in the car by manually computing mpg using actual miles driven/gallons used and comparing the result with the car's computer readout (after resetting it before the comparison)? I suspect the car's computer is fairly accurate, but I really don't have any proof.

Jud

Domsz06
04-29-11, 02:03 PM
dead on when I tested it.

Cub Cadet
04-29-11, 04:06 PM
Yes, the computer is 100% correct. The trick to keeping it 100% correct is to reset it at each fill up. You will never have any discrepancy that way.

JFJr
04-29-11, 04:28 PM
Yes, the computer is 100% correct. The trick to keeping it 100% correct is to reset it at each fill up. You will never have any discrepancy that way.Yes, I believe that if the average mpg function is not reset, it keeps a running calculation for the last 20 gallons or so. I use the range function quite a bit on long trips, but one has to be cautious when going from freeway to city driving, because the computer may show a higher (incorrect) range value depending upon the relative amount of miles spent in each scenario. Anyway, it is a useful tool given the way our gas gauge is programmed (rapid decrease above the half-tank mark and slower decrease afterwards).

neuronbob
04-29-11, 04:51 PM
Yup, just about 100% accurate.

shade
04-29-11, 06:24 PM
Interesting mine is off.
I fill up and see how many gallons go in and then come back and compare the amount put in to how many miles driven = 16.9mpg
computer shows 14.5

baabootoo
04-30-11, 02:03 AM
Interesting mine is off.
I fill up and see how many gallons go in and then come back and compare the amount put in to how many miles driven = 16.9mpg
computer shows 14.5

Did you reset it before the test? Are you checking the average also?

Caddy Wagon
04-30-11, 10:13 AM
Speaking of accuracy, does anyone know how accurate the TPMS sensors are? I was checking my air pressure yesterday, and none of the 3 gauges I have matched what the TPMS was reading.

JFJr
04-30-11, 10:19 AM
Speaking of accuracy, does anyone know how accurate the TPMS sensors are? I was checking my air pressure yesterday, and none of the 3 gauges I have matched what the TPMS was reading.My TPMS readings are approx. 2 psi below my gauge readings.

PhxTriode
04-30-11, 05:54 PM
Interesting mine is off.
I fill up and see how many gallons go in and then come back and compare the amount put in to how many miles driven = 16.9mpg
computer shows 14.5

Its the injector data being off a tad

oxymoron
04-30-11, 09:09 PM
miles gals MPG date conditions price/gal a/c on? temps comments

250 16.22 15.41 1/13/2011 hwy and commute 3.199 n 50-80 DIC said 16.0 mpg and 247 driven
279 16.95 16.46 1/22/2011 hwy and commute 3.259 y/n 50-70 DIC said 17.2 mpg and 279 miles driven
261 16.42 15.89 1/29/2011 hwy and commute 3.199 n 40-70 DIC said 16.3 MPG

Mine reads a bit optimistic sometimes.

muohio
04-30-11, 11:33 PM
I have been tracking my fuel ups on fuelly.com since getting the car and it's pretty close.

marktanner
05-02-11, 12:47 AM
I check actual mpg, and reset my compute each fill-up. It is occasionally 100% accurate, but is more often about 0.5 mpg optimistic. The computer in my '08 CTS was much more accurate.

zinner
07-27-11, 10:45 PM
Interesting mine is off.
I fill up and see how many gallons go in and then come back and compare the amount put in to how many miles driven = 16.9mpg
computer shows 14.5

Looks like you are tuned, and basically once you get tuned the MPG function is out the window in my experience.

I am stock 11 sedan and the DIC mpg readout is dead on after 1300 miles of tracking manually.

Domsz06
07-27-11, 11:02 PM
i guess I'll have to check mine now that I am tuned. It was dead on before, and last time I filled up doing a quick math in my head it was still dead on...

Doesn't a tune affect it if the tuner doesn't mess with it? I mean if the tuner adjusts your injector pulse you should still be ok (if you know your injector pulse)

Domsz06
07-27-11, 11:02 PM
Speaking of accuracy, does anyone know how accurate the TPMS sensors are? I was checking my air pressure yesterday, and none of the 3 gauges I have matched what the TPMS was reading.

mine were dead on last time I checked. Will check tomorrow.

JOEYCTS-V
07-27-11, 11:43 PM
The TPMS accuracy has mostly to do with the gauge you're using. You'll probably get a different reading with every gauge you use. Some are cheap/inaccurate and some aren't.

6speeder
07-28-11, 10:07 AM
Your tire pressure sensors will read incorrectly anywhere above sea level. At 6,000 feet mine read 4 pounds low.

Antero
07-29-11, 01:22 AM
Ive checked mine a few times and it seems to be dead on.