Fuel System Operation - CNG: Notes

WARNING: This page is about a different car, the 2003 Pontiac Sunfire, 2003 Pontiac Grand Am, 2003 Oldsmobile Alero, and 2003 Chevrolet Cavalier. However, it is still accessible from the selected car via links, so may be relevant.

This vehicles primary fuel source is Compressed Natural Gas (CNG). The vehicle will only switch-over to gasoline operation if one of the following conditions is present:

The Fuel Tank Pressure (FTP) sensor indicates CNG fuel pressure is below 200 psi (1379 kPa).
Every 100th start the vehicle will start and run briefly on gasoline. After this, a switch-over to CNG will occur during the first decel condition.
A system fault is detected by the PCM.
The engine cranks for 8 seconds and fails to start on CNG.