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) requires continuous battery voltage to operate. The TCM uses ignition voltage and or ignition accessory switch voltage for TCM wake up and operation. When ignition voltage and ignition accessory switch voltage are switched off, the TCM starts to power down. The TCM determines if battery voltage is lost prior to completion of the power down.