RPM Reference Signal
WARNING: This page is about a different car, the 2003 Pontiac Grand Prix, 2003 Chevrolet Malibu, and 2003 Buick Century. 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 sensor (Hall Effect signal, PM generator signal on DIS and IDI). These signals are used by PCM for determining control of timing, fuel delivery, EGR function and idle speed.