Overdrive Range, 4-3 Downshift - Torque Converter Clutch Not Applied (W/O Electronic Range Select Mode): Notes
WARNING: This page is about a different car, the 2008 Pontiac G5 and 2008 Chevrolet Cobalt. However, it is still accessible from the selected car via links, so may be relevant.
When the transmission is operating in Overdrive Range - Fourth Gear, a forced 4-3 downshift will occur following a significant increase in throttle position. At minimum throttle, vehicle speed will decrease gradually (coastdown) and the PCM will command a 4-3 downshift. The PCM will also initiate a 4-3 downshift if the engine load is increased while the throttle position remains the same (for example, driving up a steep hill).