Caution: Always use the J 42435-B Compressed Natural Gas (CNG) Fuel Tank Venting Kit in conjunction with the General Motors approved Fuel Tank Venting service procedure to vent CNG fuel tanks. Failure to use the J 42435-B and follow the approved Fuel Tank Venting procedure could result in death, serious injury or vehicle and component damage.

Important: 

Tools Required

J 42435-B CNG Tank Vent Kit

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



2. Remove the CNG fuel tank. Refer to Fuel Tank Replacement .

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. Disconnect the negative battery cable.
4. Remove the fuel sending unit (FSU).
5. Install the plug and the cap (4) in the FSU port (3).
6. Install the cap (1) on the fuel inlet fitting (2).



7. Connect the vent hose (1) to the fuel outlet fitting and to the vent stack.

Caution: When venting the Compressed Natural Gas (CNG) fuel tank take the following precautions in order to prevent fire and personal injury:

•	Use the proper grounding procedure to an earth ground in order to prevent a build-up of static electricity which can lead to an electrical discharge.

•	Use the J 42435-B CNG Tank Vent Kit with a vent stack.

•	Vent the CNG fuel tank in a well ventilated work area.

•	Keep sparks, flames, and smoking material away from the area.

•	Wear the appropriate hearing protection during the venting procedure. A sudden pressure loss from an uncontrolled gas leak can cause hearing damage.

8. Connect the ground strap (2) (attached to the vent hose) to the HPL and to the vent stack (earth) ground.



9. Remove the manual shut-off fitting from the HPL.
10. Verify that the manual vent tool is closed (allen screw backed out).
11. Install the manual vent tool in the HPL.



12. Slowly turn the allen screw in the manual vent tool clockwise until natural gas starts to vent. Do not leave the tank unsupervised.
13. The CNG fuel tank is completely vented when all of the following conditions have been met:

13.1.

Venting natural gas is no longer audible from the vent stack.

13.2.

Close the J 42435-B ¼-turn valve and stabilize the fuel tank and line assembly at a temperature greater than 7°C (45°F) for at least 4 hours.

If the ambient temperature is less than 7°C (45°F), warm the fuel tank and vent line assembly manually, either with warm water or by placing the tank and line assembly into a warm environment.

13.3.

The J 42435-B pressure gauge indicates 0 kPa (0 psi).

Caution: Always use the J 42435-B Compressed Natural Gas (CNG) Fuel Tank Venting Kit in conjunction with the General Motors approved Fuel Tank Venting service procedure to vent CNG fuel tanks. Failure to use the J 42435-B and follow the approved Fuel Tank Venting procedure could result in death, serious injury or vehicle and component damage.

The J 42435-B is required for the following reasons:

•	Natural gas fuel vapor can also contain water vapor.

•	The pressure drop associated with venting high pressure gaseous fuel can cause fuel vapor, tank and line temperatures to reach -73°C (-100°F) or colder.

•	The below freezing temperature can cause the water vapor to freeze

•	The J 42435-B vent hose contains an orifice which is intended to freeze before the CNG high pressure lock-off (HPL) tank valve freezes.

•	The J 42435-B pressure gauge can indicate a restricted orifice if fuel flow ceases.

•	Internal fuel tank ice build-up may result when venting the CNG fuel tank without the J 42435-B.

-	Internal fuel tank ice build-up can completely restrict the venting of fuel.

-	Venting may cease indefinitely depending upon ambient temperature conditions.

-	The ceasing of fuel tank venting may falsely indicate that the fuel tank pressure has been completely vented.

-	CNG fuel tanks with exceptionally high water content are suceptible to internal fuel tank ice build-up even with the use of the J 42435-B.

The CNG fuel tank is completely vented when all of the following conditions have been met:
1. Venting natural gas is no longer audible from the vent stack.
2. Close the J 42435-B ¼-turn valve and stabilize the fuel tank and line assembly at a temperature greater than 7°C (45°F) for at least 4 hours.

If the ambient temperature is less than 7°C (45°F), warm the fuel tank and vent line assembly manually, either with warm water or by placing the tank and line assembly into a warm environment.

3. The J 42435-B pressure gauge indicates 0 kPa (0 psi).
1. Relieve the fuel system pressure. Refer to Fuel Pressure Relief .



2. Remove the tank cover. Refer to CNG Fuel Tank Cover Replacement in Body Rear End.

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. Disconnect the negative battery cable.
4. Close the manual shut-off valve (MSV).
5. Disconnect the fuel line from the engine side of the MSV.
6. Connect the vent hose (1) to the MSV and to the vent stack.

Caution: When venting the Compressed Natural Gas (CNG) fuel tank take the following precautions in order to prevent fire and personal injury:

•	Use the proper grounding procedure to an earth ground in order to prevent a build-up of static electricity which can lead to an electrical discharge.

•	Use the J 42435-B CNG Tank Vent Kit with a vent stack.

•	Vent the CNG fuel tank in a well ventilated work area.

•	Keep sparks, flames, and smoking material away from the area.

•	Wear the appropriate hearing protection during the venting procedure. A sudden pressure loss from an uncontrolled gas leak can cause hearing damage.

7. Connect the ground strap (2) (attached to the vent hose) to either the tank-to-MSV fuel line, the MSV, or the vehicle frame, and to the vent stack (earth) ground.
8. Open the MSV.



9. Remove the manual shut-off fitting from the HPL.
10. Verify that the manual vent tool is closed (allen screw back out).
11. Install the manual vent tool in the HPL.



12. Slowly turn the allen screw in the manual vent tool clockwise until natural gas starts to vent. Do not leave the tank unsupervised.
13. The CNG fuel tank is completely vented when all of the following conditions have been met:

13.1.

Venting natural gas is no longer audible from the vent stack.

13.2.

Close the J 42435-B ¼-turn valve and stabilize the fuel tank and line assembly at a temperature greater than 7°C (45°F) for at least 4 hours.

If the ambient temperature is less than 7°C (45°F), warm the fuel tank and vent line assembly manually, either with warm water or by placing the tank and line assembly into a warm environment.

13.3.

The J 42435-B pressure gauge indicates 0 kPa (0 psi).