Conditions for Running the DTC

WARNING: This page is about a different car, the 2004 GMC Sierra and 2004 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.

DTCs P0148, P0611, or P1209 are not set.
The ignition voltage is between 6-18 volts.
The engine is operating on CNG.
The PCM is not in fuel shut-off, or decel fuel cut-off mode.