Glyn M Ruck

I have STFF and realise that people don't understand the rolling circumference of tyres but can't find what I want.

Where does the speedometer pick up it's voltage data from? Rear wheels? front wheels? ABS sensors? a transmission sensor somewhere?

Your help would be much appreciated

pshek

It picks up the data from the 4 wheel speed sensors, which are on the metal ends of the side axles. You can datalog the values by hooking them up to SDS. TCU gets the data from the wheel speed sensors and transmission output speed sensors. If there is a discrepancy between the wheel speed and the transmission output speed by more then a certain low % value, then the TCU will throw a code and put you into limp mode. You can adjust for changes in tire size diameter by setting the correct tire sizes in SDS.

Glyn M Ruck

Thanks a lot!! and TCU = what MB call TCM = Transmission Control Module?

The reason I was asking was in relation to rolling circumference of tyres. So the Star (SDS) can adjust for roll. circ. changes. Thank you - you have answered all my questions

pshek

yes, you just version code the tire size you are using. I think you need an unlocked SDS/developer mode to do it.

Glyn M Ruck

OK - I have access to such a beast - thanks