Fuel Tank Vent: Service and Repair

Compressed Natural Gas Tank Venting

Special Tools

CH-48027 - Digital Pressure Gauge

For equivalent regional tools, refer to Special Tools Tools and Equipment.

Note:
Only compressed natural gas (CNG) trained technicians should attempt this service procedure. Contact General Motors TAC for information and assistance with the following procedures.

1. Raise the vehicle. Refer to Lifting and Jacking the Vehicle Service and Repair.

2. Remove the fuel tank cover. Refer to Compressed Natural Gas Tank Cover Replacement - Aft Tank Compressed Natural Gas Tank Cover Replacement - Aft Tank , Compressed Natural Gas Tank Cover Replacement - Cargo Tank Compressed Natural Gas Tank Cover Replacement - Cargo Tank , and Compressed Natural Gas Tank Cover Replacement - Midship Tank Compressed Natural Gas Tank Cover Replacement - Midship Tank.

Note:
Do not tear the clear plastic gas venting covering. This cover prevents vapors from entering the cargo area.

3. Carefully remove the cargo tank valve plastic cover. Do not damage or discard this cover. Replace if damaged





4. If the fuel system is near empty, you may close the unaffected tank manual valves and run the vehicle until the tank is empty.

5. If not, close the unaffected tank manual valves and perform the following:

1. Remove the engine cover. Refer to Engine Cover Replacement Service and Repair.

2. Connect the CH-48027 - gaugeto the fuel rail.

3. Route the pressure relief hose into an approved vent stack attached to an area outside the building.

6. Using a fused jumper wire, jumper the fuel pump relay terminals 30 to 87 to begin the venting process. The CNG fuel tank is completely vented when all of the following conditions have been met:

* Venting gas flow is no longer audible from the vent stack.

* If ambient temperature is lower than 7°C (45°F), warm the fuel tank and vent assembly by placing in a warm environment or spraying with warm water.

7. Disconnect the negative battery cable. Refer to Battery Negative Cable Disconnection and Connection Battery Negative Cable Disconnection and Connection.

8. Loosen the high pressure fuel line fitting at the CNG fuel tank to be removed for venting several turns to allow residual system pressure to be released. Completely disconnect fitting when fuel line can be moved away from mating fitting by hand.

9. Remove the CNG fuel tank from the vehicle. Refer to Compressed Natural Gas Tank Replacement - Aft Tank Compressed Natural Gas Tank Replacement - Aft Tank , Compressed Natural Gas Tank Replacement - Cargo Tank Compressed Natural Gas Tank Replacement - Cargo Tank , or Compressed Natural Gas Tank Replacement - Midship Tank Compressed Natural Gas Tank Replacement - Midship Tank.