Shift Indicator
WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2007 GMC Yukon XL, 2007 GMC Yukon, 2007 Chevrolet Tahoe, 2007 Chevrolet Suburban, and 2007 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.
The instrument panel cluster (IPC) illuminates the shift indicator when the engine control module (ECM) determines that the vehicle should be shifted to the next higher gear. The IPC receives a class 2 message from the ECM requesting illumination.