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 panel cluster (IPC) converts the engine speed signal to a tachometer position to indicate the engine speed. The IPC also receives from the ECM a class 2 message indicating the engine speed. The IPC uses the class 2 engine speed information from the ECM for diagnostic purposes.