Conditions for Running the DTC

WARNING: This page is about a different car, the 2004 Buick Rendezvous. However, it is still accessible from the selected car via links, so may be relevant.

The ignition 1 voltage is more than 7 volts.
The TP sensor 1 voltage is between 0.18-4.6 volts.
DTC P0121 runs continuously once the above conditions are met.