Conditions for Running the DTC

WARNING: This page is about a different car, the 2007 Hummer H2. However, it is still accessible from the selected car via links, so may be relevant.

DTCs P0606, P2108, or U0107 are not set.
The ignition switch is in the Crank or Run position.
The ignition voltage is more than 5.23 volts.
DTC P2121 runs continuously once the above conditions are met.