DTC P1516: Commanded Vs. Actual Throttle Position Performance (TAC Module): 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.
The commanded throttle position is compared to the actual throttle position based on Accelerator Pedal Position (APP) and possibly other limiting factors. Both values should be within a calibrated range of each other. The Powertrain Control Module (PCM) continuously monitors the commanded and actual throttle positions. This DTC sets if the values are greater than the calibrated range.