Fuel
For diesel engine vehicles, see “Fuel for Diesel Engines” in the Duramax Diesel Supplement.
For Vehicles with gasoline engines, please read this.
See also:
Ignition Transmission Lock Check
While parked, and with the parking brake set, try to turn the ignition to LOCK/OFF in each shift lever position.
• The ignition should turn to LOCK/OFF only when the shift lever is in P (Park).
...
Fuel Additives
To provide cleaner air, all gasolines in the United States are now required to contain additives that help prevent engine and fuel system deposits from forming, allowing the emission control system to ...
Footnotes — Maintenance Schedule Additional Required Services — Normal
a) Or every two years, whichever comes first. More frequent replacement may be needed if the vehicle is driven in areas with heavy traffic, areas with poor air quality, or areas with high dust levels. ...