Shift Indicator
WARNING: This page is about a different car, the 2004 Pontiac Sunfire and 2004 Chevrolet Cavalier. 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 originating from the PCM via the BCM requesting illumination.