Hi,
I have Audi a4 b6 1.9tdi 130hp 2002y. ECU (EDC15p+) not receiving vehicle speed signal (VCDS: engine block, channel 006, and i think 23 or 33 can't remember now), but detects RPM. For example: Instrument Cluster or Climate control unit receiving vehicle speed without problem.
As far as I know, ECU receiving speed signal from Instrument cluster, so does it come through separate wire, or through CAN? Can not find any good wiring diagram for this.
You are asking about 2 different speed data. First, there is engine RPM, the ECU is the source for that data and is sent to other controllers on the CAN buss.
Vehicle road speed data originates from a speed sensor installed in the transmission (only for '02 in NA,) sent to other controllers via dedicated VSS buss circuit, or from the ABS via CAN from '01 only for Euro models.
The instrument cluster receives road speed from the ABS for display on the speedometer. The IC receives engine RPM from the ECU via CAN and displays that data on the tachometer.