Instrument Panel Cluster (IPC) Description and Operation: Speedometer
WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2003 GMC Yukon XL, 2003 GMC Yukon, 2003 Chevrolet Tahoe, 2003 Chevrolet Suburban, and 2003 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.
The IPC displays the vehicle speed on the analog speedometer based on the vehicle speed signal from the PCM. The PCM converts the data from the vehicle speed sensor to a 4,000 pulses/mile signal. The IPC uses the vehicle speed signal circuit from the PCM in order to calculate the vehicle speed. The IPC also receives a class 2 message from the PCM indicating the vehicle speed. The IPC compares the class 2 value to the vehicle speed signal from the PCM to determine if the vehicle speed is valid. When the IPC detects a malfunction in the vehicle speed signal circuit, the IPC uses the class 2 message from the PCM to indicate the vehicle speed.