Shift Indicator
WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. 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.