Tach Pulse (Rpm Reference) Signal

Connect scan tool to DLC. Scan low and high resolution reference pulses. Both high and low pulses should be present when engine is cranking or running. If low resolution pulse is not present, engine will not start and PCM will set a Diagnostic Trouble Code (DTC) in memory. If high resolution pulse is not present, vehicle will still run; however, PCM will set a DTC in memory. For circuit and terminal reference, see appropriate schematic in NO START - ENGINE CRANKS OKAY  in this article or TESTS W/CODES article.