There really is no specific RPM sensor. There is a TDC sensor at the end
of one of the camshafts that is used for ignition timing etc. The
tachometer gets its signal from the ignition system.
I don't know this to be true of this specific vehicle but many vehicles have
a crankshaft speed sensor located on the front of the crankshaft. Kind of
like how an abs sensor and sensor ring operate.