Circuit/System Description

The engine control module (ECM) creates the vehicle speed output signal by pulsing the vehicle speed signal circuit to ground at a rate of 4 KPPM. The VSS signal circuit is pulled high to B+ in the instrument panel cluster (IPC). The IPC converts the 4 KPPM vehicle speed signal to a speedometer position to indicate the vehicle speed. The ECM monitors the voltage at the vehicle speed output signal circuit to determine when the voltage is out of the normal operating range.