Circuit/System Description
WARNING: This page is about a different car, the 2019 Chevrolet Malibu. However, it is still accessible from the selected car via links, so may be relevant.
The engine control module (ECM) creates the engine speed signal by pulsing the engine speed signal circuit at a rate of 2 pulses per engine revolution. The Radio converts the 2 pulses per engine revolution signal to an engine speed value used for active noise cancellation purposes. The ECM monitors the voltage at the engine speed signal circuit to determine when the voltage is out of the normal operating range.