Speedometer: G3 Impulse Calibration Adjustment

Hello, fellow diesel enthusiasts,

I've been reading posts here from you all quite often in recent weeks and I've noticed that many people here have a lot of knowledge about the subject. Maybe you can help me with my problem.
I own a G3 (year 1996) with a 1Z engine, which doesn't have a Multifunction Display (MFA). Since I wanted to have one, I looked on eBay, but I noticed that it's very rare to find a G3 TDI speedometer with an MFA there. I then bought a speedometer from a GTI, which works fine so far (the rev counter goes up to 7500, and I'll never reach that range, but it still displays the RPM correctly). However, my (old) TDI speedometer has an odometer reading of 3819, while the (new) GTI speedometer reads 3862. This means that the mileage is being calculated incorrectly.
Using VAGCom, I obviously (unfortunately) cannot access the instrument cluster, and therefore cannot adjust the value. Does anyone know of a way to adjust the value even without VAGCom? Or should I just go to the dealership? Thank you very much!

Hi,

For those people who are driving around with tires that are too small (13-inch alloy wheels with 195-40R13 tires), there's also a speedometer adjustment that the TÜV (German technical inspection authority) requires. Maybe that could help.
Have you ever measured the difference when you've traveled a known distance?
Maybe it's so small that it's not worth it.

Regards,

Eike.

Hello,

You can also have your speedometer checked at ADAC. For members, this is (or at least was) free of charge.

Best regards, Rainer.

I've calculated that the deviation isn't as significant as I initially thought (about 1.2 km per 100 km). It's roughly accurate in practice. Still, I told a friend to check if they can adjust the wheel circumference setting on their device.
Otherwise, I have now connected the fuel consumption signal to the speedometer and I've noticed that it probably displays too much (about 1 liter/100km). However, I have only driven 6km with it , so I will only be able to really tell if it's displaying too much on the trip to Berlin this weekend (or when I fill up the tank next time...).
Thank you for your tips, and have a nice evening .