Originally Posted by JimBlake
OBD-1 flashing-lignt code 17 is for VSS.
OBD-2 scanner code P0500 is VSS for MT cars.
OBD-2 code P1791 is VSS for AT cars.
It may be that only certain cars ECU watches the VSS. For example without a VSS signal it won't engage VTEC; so maybe that means a non-VTEC ECU doesn't care whether the VSS is present or not? AT cars since maybe '94 use the VSS to decide shifting strategies.
I'm not sure about that, my point was just that the MIL on OBD2 cars is generally for emissions only and that sometimes if the problem doesn't cause an emissions issue the ECU won't light a MIL or store a DTC. It's not common but it happens.