RPM Reference Signal
WARNING: This page is about a different car, the 2003 Pontiac Vibe. However, it is still accessible from the selected car via links, so may be relevant.
The RPM is monitored by PCM through tach/pulse signals produced by either the ignition control module or Crankshaft Position (CKP) sensor, Hall Effect signal, PM generator signal on DIS. These signals are used by the PCM for determining control of timing, fuel delivery, EGR function and idle speed.