DTC P1515: Predicted Vs Actual Throttle Position Correlation Error: Description
WARNING: This page is about a different car, the 2003 Chevrolet Corvette. However, it is still accessible from the selected car via links, so may be relevant.
The commanded throttle position, based on accelerator pedal position and possibly on other limiting factors, is compared to the actual throttle position. The 2 values should be within a calibrated range of each other. Both the Powertrain Control Module (PCM) and the Throttle Actuator Control (TAC) module redundantly monitor the commanded and actual throttle position. This DTC sets if the PCM detects an out-of-range condition between the commanded and the actual pedal position.