GMC Sierra Owners Manual
Charging System Light
This light comes on briefly when the ignition key is turned to START, but the engine is not running, as a check to show it is working.
If it does not, have the vehicle serviced by your dealer.
The light should go out once the engine starts. If it stays on, or comes on while driving, there could be a problem with the charging system. A charging system message in the Driver Information Center (DIC) can also appear. See Battery Voltage and Charging Messages on page 5‑43 for more information. This light could indicate that there are problems with a generator drive belt, or that there is an electrical problem. Have it checked right away. If the vehicle must be driven a short distance with the light on, turn off accessories, such as the radio and air conditioner.
If the vehicle is a hybrid, see the hybrid supplement for more information.