My 2008 Fortwo is giving me code P0500 Speed sensor A. Not sure which is speed sensor A but I checked the sensor on the tranny and that seems to work fine, it breaks the circuit when you push the button. The wheel sensors I can't figure out. They all seem to have the same resistance but nothing changes when you spin the wheel. I tried measuring voltage, AC & DC and resistance and got nothing to change when I spin the wheel. It drives fine the speedo works and it shifts fine. Anyone know how to test these?