Upshift Indicator
WARNING: This page is about a different car, the 2007 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
The body control module (BCM) receives a controlled area network (CAN) serial data message from the engine control module (ECM) when the ECM determines that the vehicle should be shifted to the next higher gear. The instrument panel cluster (IPC) illuminates the shift indicator when the BCM sends a class 2 message requesting illumination.