Conditions for Setting the DTC: P2123
WARNING: This page is about a different car, the 2007 Pontiac G5 Pursuit, 2007 Pontiac G5, and 2007 Chevrolet Cobalt. However, it is still accessible from the selected car via links, so may be relevant.
The ECM detects that the APP sensor 1 voltage is more than 4.87 volts for more than 0.4 second.