Circuit/System Description

The engine control module creates the engine speed signal by pulsing the engine speed signal circuit to ground at a rate proportional to engine revolution speed. The Instrument Panel Cluster Control Module converts the engine revolution signal to a tachometer position indicating the engine speed. The engine speed is sent to the Instrument Panel Cluster Control Module over a discreet wire from the engine control module. The tachometer signal is pulled up to B+ in the Instrument Panel Cluster Control Module. 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.