VAG-Com Speed Accuracy: Measuring Block Details

Hello everyone.

Control unit information: 038 906 019 KP, "1.9l R4 EDC 0000SG 4902"

How accurate is the speed display in VAG-COM? It's clear that this depends on the tire size used and the rolling circumference. Has anyone compared it to GPS data?
I've generally found that GPS devices perform slightly better under optimal conditions in terms of GPS signal strength and accuracy (with an accuracy of around 7-10 meters).
Even with GPS, the update rate is usually faster, although only one data block is displayed. I believe you can only get accurate measurements over longer distances.
What are your experiences regarding this?

Best regards,

To my knowledge, the signal comes from the combination instrument. You can also see the unfiltered signal there. In the instrument cluster, it is calculated based on the K-value and the characteristic curve (including advance and deviation) and then passed on, for example, to the 'pointer' for display.

hello

The combined instrument or wheel speed data should be coming from the ABS control unit via CAN bus or an internal bus to the engine control unit (ECU). If I've established a connection to the engine electronics and am querying the value from measurement block 5 or 6, is that data already filtered? I'll also check the value from the combined instrument again and log both, then compare them.
Thank you in advance.

best regards
Rene.

hello

The combination instrument, or the wheel speed, should come from the ABS control unit via CAN or an internal bus to the engine control unit .

Not with the vehicle mentioned. It has a sensor in the transmission that connects directly to the instrument cluster.

Okay, that's useful information. So, does the transmission handle the speed signal for the speedometer and the measurement output? In other words, the ABS control unit doesn't pass anything on, but only uses the measured wheel speeds for its own functions and for the ESP? And the engine control unit also receives information from the ESP, such as when the wheels are spinning, etc.
It's noticeable that when the wheels are spinning, the accelerator pedal no longer has any effect.

Yes, that's a good piece of information. So, is the speed information for the speedometer or measurement output derived from the transmission?

Not intercepted, the sender is a pulse generator and 'creates' the signal for the AI. It is then converted using the k-value and characteristic curve, and further distributed. The difference in output varies between 5...8...10 km/h, depending on the pre-setting and the current k-value.