Circuit/System Description

The engine control module (ECM) creates the vehicle speed signal by pulsing the vehicle speed signal circuit to ground at a rate of 4KPPM. The instrument panel cluster (IPC) converts the 4KPPM vehicle speed signal to a speedometer position to indicate the vehicle speed. The IPC also receives from the ECM a class 2 message indicating the vehicle speed. The IPC uses the class 2 vehicle speed information from the ECM for diagnostics purposes.