DTC P1682: Driver 5; Line 2: 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 Throttle Actuator Control (TAC) system uses an ignition voltage supply separate from the PCM supply. If PCM detects a voltage difference between the 2 circuits, this DTC will set.