3X REF Low

This is a ground circuit for the digital RPM counter inside the PCM, but the wire is connected to engine ground only through the ignition control module. Although this circuit is electrically connected to the PCM, it is not connected to ground at the PCM. The PCM compares voltage pulses on the reference input circuits to pulses on this circuit, ignoring pulses that appear on both. Refer to Electronic Ignition System for further information.