Tach Pulse (RPM Reference) Signal
WARNING: This page is about a different car, the 1995 Oldsmobile Aurora and 1995 Buick Riviera. However, it is still accessible from the selected car via links, so may be relevant.
Connect scan tester to DLC. RPM should be indicated on tester when engine is cranked or running. Tach pulse (RPM reference) will be indicated as a voltage signal when a DVOM (with a minimum 10-megohm input impedance) is used to backprobe circuit No. 430 PCM terminal. For circuit and terminal reference, see appropriate schematic in NO START - ENGINE CRANKS OKAY.