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Dieselgate - VW Group Emission Scandal Discussion around the VW Dieselgate Emissions scandal. Details and news updates can be viewed here: http://forums.tdiclub.com/showthread.php?goto=newpost&t=448336 This forum is a work in progress depending on requirements, usage, etc.

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Old February 13th, 2018, 08:02   #1
tsspencer2887
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Default Computer MPG vs Hand Calc after the fix

This may be an old topic but I didn't find anything about it. If so, please refer me to that thread and delete this one.

I had the fix on my 2011 Sportwagen 6MT a few weeks ago but I haven't been the one to refill the tank yet. Others in my family have taken it on some long road trips but they don't know how to reset the computer. Prior to the fix, the computer showed ~1-1.5 MPG higher than hand calc. My Dad drove the car on a trip a week ago and swears that I'll be lucky to get 40 MPG now. However I took it on a short trip (~150 miles) and the computer's MPG had me averaging ~48-49 MPG.

I'll know how far off the computer is the next time I fill up but I don't know when my next long range trip will be. Is there any reason that the computer should be further off now than it was before? Just wondering if anyone has noticed a difference.
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Old February 13th, 2018, 09:27   #2
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I have recorded both computer averages and hand calculated averages per tank since buying my 2009 new. After the fix (in October), the computer is off 2 to 4 mpg (higher than hand calculated) vs .5 to 1.5 before. This is all based on routine mixed driving in Indianapolis. It will be interesting to do a long highway trip and see the numbers then.
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Old February 13th, 2018, 09:33   #3
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I’m a different TDI model & generation, but the MFD on mine typical shows 2 to 2.5 mpg (roughly 4%) higher than actual, and I record every tank on Fuelly. I haven’t tried correcting with VCDS because it’s not that important to me honestly.
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Old February 13th, 2018, 10:43   #4
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It is possible but only you will know when checked. If you are near Austin I have VCDS and we can reset it so it shows near actual once you find the setting you need. Who really cares what the computer says if it is wrong? Take some trips and find the number and get it reset so its closer. All highway vs all city will show different results as well in my experience.
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Old February 13th, 2018, 15:44   #5
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Only had a 2010 Jetta TDI and it was 0.5-1mpg off without the fix. My new 2015 Passat TDI with the fix is 2-4mpg off from what I've noticed, but I haven't had a true full fill up. Right now I have 2 more days of driving and I'll have to fill up. Assuming nothing happens between now and then, I'll be able to give a real answer.
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Old February 13th, 2018, 16:21   #6
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This shouldn't be based on one tank but several at least. (redacted) Read that wrong.
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Old February 14th, 2018, 07:07   #7
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Thanks for the input. All of my day to day driving involves rush hour traffic in DFW (aka "the metromess"). So I typically average 36-37 MPGs (hand-calc). However, we have a trip coming up to Florida next month and are deciding between taking my Jetta or my mother's far more comfortable yet much less fuel economic ML350.
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Old February 15th, 2018, 09:50   #8
Q5TDI
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How does the computer calculate the mpg and mileage left before an empty tank?
When I would fill up my 2014Q5 TDI pre-fix, the computer would often tell me I could go 650 miles before the tank went empty. I would be lucky to go just over 600 miles in most cases, and in several cases, I could only go 500-525 miles.

Still, by hand calculation, my TDI consistently got 29-31 mpg, which is what the computer would tell me for the overall mpg since I bought the car. I drive about 50/50 highway and around town.

I would never base mpg of the instantaneous mpg number, which can fluctuate between 5 mpg and over 200 mpg, depending on if the car is going uphill, downhill, accelerating, etc.
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Old February 15th, 2018, 11:55   #9
forrest resto`s
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Quote:
Originally Posted by tsspencer2887 View Post
This may be an old topic but I didn't find anything about it. If so, please refer me to that thread and delete this one.

I had the fix on my 2011 Sportwagen 6MT a few weeks ago but I haven't been the one to refill the tank yet. Others in my family have taken it on some long road trips but they don't know how to reset the computer. Prior to the fix, the computer showed ~1-1.5 MPG higher than hand calc. My Dad drove the car on a trip a week ago and swears that I'll be lucky to get 40 MPG now. However I took it on a short trip (~150 miles) and the computer's MPG had me averaging ~48-49 MPG.

I'll know how far off the computer is the next time I fill up but I don't know when my next long range trip will be. Is there any reason that the computer should be further off now than it was before? Just wondering if anyone has noticed a difference.
I never got 48 49 mpg's on my 2011 jetta 6mt..before the fix and surely not after.. on a road trip i may get 43 if I'm lucky...hand calc.
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Old February 15th, 2018, 15:23   #10
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Actually, the best I've ever gotten in this car was 52 MPG (hand calc).
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Old February 15th, 2018, 18:02   #11
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I just filled up and I ended up with 823.6 miles this tank. Odometer said 51.7mpg but hand calculated I got 48.5, which is in line with the 2-4 mpg difference I usually get. I did drive a lot slower and kept most of my speed at 70 mph and there was a few days I would do 65 on the way home just because I didn’t have to pick my daughters up and wasn’t in a rush.


I ended up driving about 8 miles once I hit 0 just bc I wanted to fill up at the same place. I know this car has an 18 1/2 gallon tank and usually the max I am able to put in there is 17 gallons so I wasn’t worried about driving a little once I hit zero.

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Old February 22nd, 2018, 07:03   #12
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Filled up last night and the computer overestimated ~2 mpg. At least 75% of the tank was rush hour traffic. I ended up getting about the same as I averaged in the same traffic prior to the fix.
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Old February 22nd, 2018, 13:31   #13
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Quote:
Originally Posted by tsspencer2887 View Post
Filled up last night and the computer overestimated ~2 mpg. At least 75% of the tank was rush hour traffic. I ended up getting about the same as I averaged in the same traffic prior to the fix.
I appreciate your comparative fuelly accounts - thank you. My 2011 JSW manual nets me ~31mpg in mostly city driving (yeah, I know) though it's been down almost 2 since I've left my roof racks on. No fix yet, part of the waffling undecided.
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Old February 22nd, 2018, 14:24   #14
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Quote:
Originally Posted by Smashed Ixnay View Post
I just filled up and I ended up with 823.6 miles this tank. Odometer said 51.7mpg but hand calculated I got 48.5, which is in line with the 2-4 mpg difference I usually get. I did drive a lot slower and kept most of my speed at 70 mph and there was a few days I would do 65 on the way home just because I didn’t have to pick my daughters up and wasn’t in a rush.


I ended up driving about 8 miles once I hit 0 just bc I wanted to fill up at the same place. I know this car has an 18 1/2 gallon tank and usually the max I am able to put in there is 17 gallons so I wasn’t worried about driving a little once I hit zero.
Is there a way to get the trip computer to run an average from reset to reset like every other vehicle I've ever had? My MPG is always started upon starting the car. It will continue the same trip if the car is stopped and started within a certain amount of time. I have always run the averages from fuel fill to fuel fill so I would know how inaccurate the computer is.
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Old February 22nd, 2018, 15:06   #15
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Quote:
Originally Posted by Quincy View Post
Is there a way to get the trip computer to run an average from reset to reset like every other vehicle I've ever had? My MPG is always started upon starting the car. It will continue the same trip if the car is stopped and started within a certain amount of time. I have always run the averages from fuel fill to fuel fill so I would know how inaccurate the computer is.
When you reset your trip odometer it resets the “mpg since refuel” readout.
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