Conditions for Setting the DTC
WARNING: This page is about a different car, the 2006 Pontiac Montana SV6, 2006 Chevrolet Uplander, and 2006 Buick Terraza. However, it is still accessible from the selected car via links, so may be relevant.
The PCM/ECM detects low voltage on the stop lamp supply voltage circuit when the circuit should be battery positive voltage.