Circuit/System Description

The Engine Control Module 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 Engine Control Module. The tachometer signal is pulled up to B+ in the Instrument Cluster. The Engine Control Module monitors the voltage at the engine speed signal circuit to determine when the voltage is out of the normal operating range.