3rd Accumulator Exhaust Checkball (#7)
WARNING: This page is about a different car, the 2008 GMC Sierra and 2008 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
After the downshift is completed, the #7 checkball unseats and allows the residual fluid in the 3rd accumulator fluid circuit to exhaust.