RPM Reference Signal
WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 2003 Pontiac Grand Prix, 2003 Pontiac Bonneville, 2003 Chevrolet Monte Carlo, 2003 Chevrolet Impala, and 2003 Buick Regal. 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 (ICM) or Crankshaft Position (CKP) 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.