Fuel gauge not accurate? 3 gal mystery

The good news is that I am now able to adjust the fuel gauge needle up an down via vcds. I have some more experimentation to do, and measuring (via Advanced measurements), but this puts me on the right track in the event that VW comes back and says that having 2-3gal of diesel left in the tank after the needle hits "0" is done by design, or that having the needle drop 1/16 from Full after 20mi of driving is normal. Any vcds adjustments would all be done of course, and if I do it, at my own risk specially given all the comment contributions above.

What I am experiment with is no different from what's described here:
http://www.myturbodiesel.com/wiki/mpg-gauge-correction-and-adjustment-mk5-mk6-vw/

(1) Offset for tank calibration values - Offset sensor 1: from -12.8l to +2l
Range is -12.8 to +8.
-12.8l is the factory default.
<0 moves the needle down.
=0 no change/movement
>0 move needle up.
+1 = needle moves up by ~1/16 up
+2 = needle moves up by ~1/8 up

I was also able to play with and adjust the MFD MPG reading to now be within +/-1 of the actual, vs ~+5 to +6 on the optimistic side from factory. That one seems like a safe change.

Thanks again for everyone who has and continues to post. I'll update this thread once I get an answer from the dealer on the current accuracy of the fuel gauge. I did find a similar person in the UK with the same issue (from another forum), and VW ended up replacing his pump due to faulty readings. Who knows, maybe there is an actual problem causing this on my car.

Interested in where you found the adjustment for MFD MPG

midntdi said:

Interested in where you found the adjustment for MFD MPG

Click to expand...

It is under:
Instruments -> Adaptation ->Display correction of consumptions and operating range

The default from factory is 100%. VCDS tells you the allowable range on that screen. In my case I settled on 106%. The MPG figures (since refuel/start/extended) all get updated on-the-fly as you apply the change. I happened to know what my real world MPG was from Fuelly.com based on ~4000mi worth of logging, so I simply changed the above setting until the extended MPG figure on the MFD matched Fuelly.

This change, in case you are wondering, has no effect on the Range figure (miles before refuel) on the Stereo or MFD, nor the fuel gauge.

I have this same issue on my car. My mk6 TDI would consistently take 12+ gallons during fill up, the best I could do was 10.19 on the mk7. The dealer is looking into it, but they didn't seem confident there was much they could do. I contacted vw on their online chat thing and they said the reserve is 1.3 gallons and that i should make a service appointment.

If I drive mine until range hits 0 and then go fill up, I can get almost 47L in or 12.4Gal.

danzola said:

The good news is that I am now able to adjust the fuel gauge needle up an down via vcds. I have some more experimentation to do, and measuring (via Advanced measurements), but this puts me on the right track in the event that VW comes back and says that having 2-3gal of diesel left in the tank after the needle hits "0" is done by design, or that having the needle drop 1/16 from Full after 20mi of driving is normal. Any vcds adjustments would all be done of course, and if I do it, at my own risk specially given all the comment contributions above.
What I am experiment with is no different from what's described here:
http://www.myturbodiesel.com/wiki/mpg-gauge-correction-and-adjustment-mk5-mk6-vw/
(1) Offset for tank calibration values - Offset sensor 1: from -12.8l to +2l
Range is -12.8 to +8.
-12.8l is the factory default.
<0 moves the needle down.
=0 no change/movement
>0 move needle up.
+1 = needle moves up by ~1/16 up
+2 = needle moves up by ~1/8 up
I was also able to play with and adjust the MFD MPG reading to now be within +/-1 of the actual, vs ~+5 to +6 on the optimistic side from factory. That one seems like a safe change.
Thanks again for everyone who has and continues to post. I'll update this thread once I get an answer from the dealer on the current accuracy of the fuel gauge. I did find a similar person in the UK with the same issue (from another forum), and VW ended up replacing his pump due to faulty readings. Who knows, maybe there is an actual problem causing this on my car.

Click to expand...

Any update on this?

Driving slightly past 0mi in my 2015 I can only eek 11.5gal into the tank at most. So that technically leaves just under 2 gal left. I'd love to utilize one more gallon that's always laying in there and make the 1gal remaining the "reserve".

In my many mk4's you could in a pinch drive ~80mi with the fuel light on. I'm assuming the engineers of the mk7 made the "0mi" remaining be approx the same as the mk4 fuel light coming on.

psd1 said:

And to the second point, does the pump really create so much heat as to need 2-3 gallons to "cool" it? nah!

Click to expand...

I suspect that part of the issue is that they do not want you to EVER run the tank dry because the lack of fuel (which is also a lubricant) could destroy the very expensive high pressure fuel pump.

But it is also true that the fuel around the pump is the primary means of cooling the electric fuel pump motor.

Lots more range with my A4 Jetta......than my MK7 GSW. Better mpg with Jetta AND with the "vent trick" can get more fuel in......i.e. lots better range on the Jetta.

danzola said:

The good news is that I am now able to adjust the fuel gauge needle up an down via vcds. I have some more experimentation to do, and measuring (via Advanced measurements), but this puts me on the right track in the event that VW comes back and says that having 2-3gal of diesel left in the tank after the needle hits "0" is done by design, or that having the needle drop 1/16 from Full after 20mi of driving is normal. Any vcds adjustments would all be done of course, and if I do it, at my own risk specially given all the comment contributions above.
What I am experiment with is no different from what's described here:
http://www.myturbodiesel.com/wiki/mpg-gauge-correction-and-adjustment-mk5-mk6-vw/
(1) Offset for tank calibration values - Offset sensor 1: from -12.8l to +2l
Range is -12.8 to +8.
-12.8l is the factory default.
<0 moves the needle down.
=0 no change/movement
>0 move needle up.
+1 = needle moves up by ~1/16 up
+2 = needle moves up by ~1/8 up
I was also able to play with and adjust the MFD MPG reading to now be within +/-1 of the actual, vs ~+5 to +6 on the optimistic side from factory. That one seems like a safe change.
Thanks again for everyone who has and continues to post. I'll update this thread once I get an answer from the dealer on the current accuracy of the fuel gauge. I did find a similar person in the UK with the same issue (from another forum), and VW ended up replacing his pump due to faulty readings. Who knows, maybe there is an actual problem causing this on my car.

Click to expand...

Was there a security key needed for the change?

Mine is on the other side of the spectrum. I can get close to 13 gallons to go in when the range gets to "0 miles remaining." That's topping off to the very top. Would be interesting to know how much useable is really left.

FreezingInSask said:

If I drive mine until range hits 0 and then go fill up, I can get almost 47L in or 12.4Gal.

Click to expand...

47L was my maximum.

marcusku said:

Mine is on the other side of the spectrum. I can get close to 13 gallons to go in when the range gets to "0 miles remaining." That's topping off to the very top. Would be interesting to know how much useable is really left.

Click to expand...

That's my experience as well. I have 32 fill-ups over 12 gallons, with my best at 12.975 gal (see my Fuelly info). I don't think I've ever driven the range down to less than 20-25 mi. I do top off slowly for the last gallon or so until I see foam, but I don't take the time to fill it to the brim.