Circuit/System Verification
WARNING: This page is about a different car, the 2007 GMC Sierra and 2007 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
With the engine ON, engage the RSM Plus/Minus switch positions while observing the Driver Shift Request parameter in the body controls scan tool data list. The parameter should change to reflect the selected Up or Downshift switch position and with no Up or Downshift switch position selected the parameter should display None.