It only applies to 2005.5+ cars and you must have a VCDS tool or let the dealer do it. If the mpg meter is inaccurate, it could also be due to larger or smaller tires/wheels than stock. See 1000q: tire, wheel, gearing calculator to see the effect of larger wheels on display mpg. Also make sure you're filling the fuel tank to the same exact level each time or else the hand calculated mpg reading will be off. Some fuel pumps also click off at different levels.
If you change the distance impulse number, it also changes the odometer, speedometer, and mpg reading, so do the mpg display accuracy test last. I suggest logging mpg over many tanks to get an idea of the average error before changing this setting.
1 Ross tech VCDS cable and software
Plug the VCDS into the obd2 port and look for the green light. Start the
software and click "Select" to get to the control modules. Click on
Click on "Adaptation-10".
Go to channel 03 by clicking "Up". Change the stored value
between 85 and 115 to adjust the fuel economy gauge calculation higher or lower
Click "Save" and then "Done". Go back to the previous screen and select "Close controller" to exit.
Sometime around 2009 or 2010 (probably 2010), VW changed the
menu. Open the dropbox and select "display correction of consumptions
and operating range". It's adjustable above or below 100%. To
lower the displayed mpg, increase the value above 100. To increase the
displayed mpg, lower the value below 100. Click "Do it!" to save.
The other option adjusts the fuel tank gauge needle higher or lower.
According to Dana at Ross tech, the max/min values are 10/-10. 10
raises the needle about 1/16 tank and -10 lowers the needle about 1/16
tank. With a full tank, the fuel tank sender should read 70 ohm. An
empty tank should read 270 ohm. These can also be read through advanced
measuring values "Fuel level sensor 1(138)".
Do you know what some of these climatronic codes are? Please share in the forums.