GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 GMC K Sierra - 4WD (CNG) 🢒 Engine 🢒 Engine Controls - 6.0L 🢒 Fill Line Union (Check Valve) Replacement

Fill Line Union (Check Valve) Replacement Pickup with Type 2 Tank

Tools Required

J 45878 Combustible Gas Detector

Removal Procedure

    Caution: Natural gas is highly flammable. In order to reduce the risk of fire and personal injury, keep sparks, flames, and smoking materials away from the vehicle while you perform the Compressed Natural Gas (CNG) fuel system service.

    Caution: The Compressed Natural Gas (CNG) system operates at pressures up to 24820 kpa (3600 psi). Relieve the CNG fuel system pressure before servicing CNG fuel system components in order to reduce the risk of fire and personal injury.

  1. Relieve the fuel system pressure. Refer to Fuel Pressure Relief .

    2. Caution: Unless directed otherwise, the ignition and start switch must be in the OFF or LOCK position, and all electrical loads must be OFF before servicing any electrical component. Disconnect the negative battery cable to prevent an electrical spark should a tool or equipment come in contact with an exposed electrical terminal. Failure to follow these precautions may result in personal injury and/or damage to the vehicle or its components.

  2. Disconnect the negative battery cable. Refer to Battery Negative Cable Disconnection and Connection in Engine Electrical in the C/K Pickup service manual.

    3. Object Number: 757009 Size: SH
  3. Remove the tank cover (2). Refer to Fuel Tank Cover Replacement .

    4. Object Number: 1489671 Size: SH
  4. Disconnect the fill line (6) from the check valve (5).
  5. Disconnect the check valve (5) from the tee (3).
  6. Remove the fill line check valve from the vehicle.

Installation Procedure

    Caution: Natural gas is stored under high pressure. If a leak occurs, the high pressure could cause a personal injury. In order to prevent Compressed Natural Gas (CNG) fuel leaks, always replace the CNG fuel system O-rings during service.


    Object Number: 1489671 Size: SH
  1. Connect the fuel fill line check valve (5) to the HPL tee fitting (3) with a new O-ring face seal. Lubricate the O-ring face seal with petroleum jelly.

    2. Tighten
    Tighten the fitting to 24 N·m (18 lb ft).

  2. Connect the fuel fill line (6) to the check valve (5) with a new O-ring face seal. Lubricate the O-ring face seal with petroleum jelly.

    3. Tighten
    Tighten the fitting to 24 N·m (18 lb ft).

    Caution: Unless directed otherwise, the ignition and start switch must be in the OFF or LOCK position, and all electrical loads must be OFF before servicing any electrical component. Disconnect the negative battery cable to prevent an electrical spark should a tool or equipment come in contact with an exposed electrical terminal. Failure to follow these precautions may result in personal injury and/or damage to the vehicle or its components.

  3. Install the negative battery cable. Refer to Battery Negative Cable Disconnection and Connection in Engine Electrical in the C/K Pickup service manual.
  4. Start the vehicle and inspect for CNG fuel leaks at the serviced fittings using the J 45878 or an equivalent liquid leak detector.

    5. Object Number: 757009 Size: SH
  5. Install the tank cover (2). Refer to Fuel Tank Cover Replacement .