Originally Posted by
blindsquirrel
Not that it really matters, I'm just curious now if the ECM is reading actual frequency to derive the RPM value or if it's looking at an average voltage over some period of time and then doing a conversion. The EV fan system is not exactly a high precision/accuracy thing like the CKP. The diagram just shows the signal input at the ECM with an internal pulldown resistor, then from there it heads off to who knows where, some undocumented magic happens, and then 'RPM' comes out the other end.