Engine Control Module (ECM)
WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2010 GMC Yukon XL, 2010 GMC Yukon, 2010 Chevrolet Tahoe, 2010 Chevrolet Suburban, and 2010 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.
The ECM directly controls the generator field control circuit input to the generator. The ECM receives control decisions based on messages from the BCM. It monitors the generators generator field duty cycle signal circuit and sends the information to the BCM.