Circuit/System Description
WARNING: This page is about a different car, the 2009 GMC Sierra, 2009 GMC Cab & Chassis Sierra, 2009 Chevrolet Silverado, and 2009 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The transmission control module (TCM) will wake up from sleep mode when a voltage greater than 5 V is detected on the switched ignition input or accessory/wake up input. The Body Control Module (BCM) provides voltage to the TCM accessory/wake up input. After wake up, the TCM will not go into sleep mode until the accessory/wake up input and ignition input are less than 5 V.