DTC P1516: Commanded & Actual Throttle Position Malfunction: Description
WARNING: This page is about a different car, the 2002 Pontiac Firebird and 2002 Chevrolet Camaro. However, it is still accessible from the selected car via links, so may be relevant.
The commanded Throttle Position (TP), based on Accelerator Pedal Position (APP) and possibly other limiting factors, is compared to the actual throttle position. The TP values should be within a calibrated range of each other. The Throttle Actuator Control (TAC) module monitors the commanded and actual throttle position. This DTC sets if the TAC module detects the condition and send the message to the Powertrain Control Module (PCM) across serial data.