Circuit/System Description

The engine control module (ECM) creates the engine speed signal by pulsing the engine speed signal circuit to ground at a rate of 2 pulses per engine revolution. The Instrument Cluster converts the 2 pulses per engine revolution signal to a tachometer position indicating the engine speed. The engine speed is sent to the Instrument Cluster over a discreet wire from the ECM. The tachometer signal is pulled up to B+ in the IPC. The ECM monitors the voltage at the engine speed signal circuit to determine when the voltage is out of the normal operating range.