Instrument Panel Cluster (IPC) Description and Operation: Speedometer
WARNING: This page is about a different car, the 2002 Chevrolet Malibu. However, it is still accessible from the selected car via links, so may be relevant.
The IPC displays the vehicle speed based on the information from the PCM. The PCM converts the data from the vehicle speed sensor to a 4000 pulses/mile signal. The IPC uses the vehicle speed signal circuit of 4000 pulses/mile from the PCM in order to calculate the vehicle speed. The speedometer defaults to 0 km/h (0 mph) if a malfunction in the vehicle speed signal circuit of 4000 pulses/mile exists or if the BCM sends or receives invalid data with the IPC via serial peripheral interface (SPI).