Shift Indicator
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 illuminates the shift indicator when the PCM determines that the vehicle should be shifted to the next higher gear. The IPC receives a class 2 message from the PCM requesting illumination.