Circuit/System Description
WARNING: This page is about a different car, the 2006 Chevrolet Monte Carlo and 2006 Chevrolet Impala. However, it is still accessible from the selected car via links, so may be relevant.
The accessory voltage signal circuit is a positive voltage signal to wake up the engine control module (ECM) and the transmission control module (TCM). The signal is activated in 2 ways. Any time the ignition switch is in the ACC or RUN position, or anytime the body control module (BCM) determines that communication is needed from the powertrain. When the ignition switch is in the ACC or RUN position, the input to the BCM is internally connected to the accessory voltage signal circuit, and voltage is supplied. The BCM supplies voltage to the accessory voltage signal when it determines that communication is necessary with the powertrain and the ignition is not in the ACC or RUN position such as during remote start.