DTC P1523: Throttle Closed Position Performance: Description
WARNING: This page is about a different car, the 2003 Oldsmobile Bravada, 2003 GMC Envoy XL, 2003 GMC Envoy, and 2003 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.
During Battery Saver Mode, the Powertrain Control Module (PCM) determines if the throttle plate is returning to the correct de-energized position. If the PCM determines the throttle plate is not at the correct position during battery saver mode, this DTC is set.