GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2003 🢒 GMC C Sierra - 2WD (CNG) 🢒 Instrument Panel 🢒 Warning Lights, Gages and Indicators 🢒 Periodic Gasoline Operation

Notice: If you do not operate your bi-fuel vehicle on one full tank of gasoline at least every 60 days, your fuel system could be damaged. Always fill the tank with gasoline at least once every two months.

To operate your bi-fuel vehicle on gasoline, do the following:

  1. Fill the gasoline fuel tank.
  2. Operate your vehicle until the CNG fuel tank is empty. The vehicle will then switch to gasoline operation.
  3. Operate the vehicle until the gasoline fuel tank is almost empty.

To return to CNG operation, do the following:

  1. Refill both the CNG and the gasoline fuel tanks.
  2. Start your vehicle. See "Starting Your Bi-Fuel Vehicle" under Starting the Vehicle .

If Your Vehicle Starts on Gasoline or Switches to Gasoline While Driving

Your bi-fuel vehicle is designed to start and operate on natural gas. However, if any one of the following conditions exist, your vehicle will start on or switch to gasoline:

    • The CNG fuel tank is empty and the low fuel indicator light on the fuel gage is on.
        Recommended Action: Fill the natural gas tank. Refer to Filling the CNG Fuel Tank .
    • Your vehicle will start on gasoline every 100th start.
        Recommended Action: Drive your vehicle for several minutes. Your vehicle will return to CNG automatically.
    • The engine crank time is more than eight seconds.
        Recommended Action: Turn the ignition to LOCK, wait several seconds and start over. If the engine does not start on CNG after three tries, take your vehicle to an authorized GM dealer for service.
    • An Alternative Fuel System (AFS) fuse is bad.
        Recommended Action: Check the AFS fuses. See Fuses and Circuit Breakers .
    • The OBD (On-Board Diagnostic) system detects a specific emission problem. The Malfunction Indicator Lamp (Check Engine Light) will come on. See "Malfunction Indicator Lamp" in the Index of your owner's manual for more information.
        Recommended Action: Your vehicle may require service. Take your vehicle to an authorized GM dealer for service.
    • A CNG fuel system problem is detected.
        Recommended Action: Turn the ignition to LOCK, wait several seconds and start again. If the engine does not start on CNG after three tries, take your vehicle to an authorized GM dealer for service.