CNG Tank Fuel Pressure Release
WARNING: This page is about a different car, the 2003 GMC Sierra, 2003 GMC Savana, 2003 Chevrolet Silverado, and 2003 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.
CAUTION:
Fuel system is under pressure. Pressure must be released prior to servicing fuel system.
- Start and operate engine at idle. Ensure engine is operating on CNG by observing that the Fuel Indicator Lamp (FIL) is off and the AFO Enable on scan tool display indicates engine is operating on alternative fuel.
- Using scan tool, select the High Pressure Lock-Off (HPL) solenoid special function.
- While engine is operating on CNG, command the HPL solenoid off and observe fuel tank pressure sensor data parameter. Fuel tank pressure should slowly decrease. If fuel pressure fails to decrease, go to step 5. When engine stalls or a switchover to gasoline is observed, go to next step.
- Turn ignition off. Remove the ALT FUELS fuse to disable the CNG fuel system. A small amount of CNG will remain in fuel lines and components. Slowly open the fittings in order to release any remaining pressure when disconnecting a fuel line. Fuel pressure relief for the CNG system is now complete. If service requires that the CNG fuel tanks to be relieved of all internal pressure, refer to CNG FUEL TANK VENTING PROCEDURE .
- Close the manual lock-down screw located on the end of each High Pressure Lock-Off (HPL) solenoid. The manual shut-off fitting is closed by rotating the Allen screw clockwise until fully seated. See Fig 1.
- Turn ignition off. Disconnect negative battery cable. Slowly loosen the fuel line fitting at the lock-off solenoid elbow several turns. Fuel pressure relief for the CNG system is complete when fuel line can be pulled away from the "O" ring face seal and fuel does not vent.
- When reinstalling, ALWAYS replace "O" ring face seals at all fittings that were disconnected or loosened. After repairs are complete, tighten any loosened fittings to correct torque. Leave manual lock-down screws closed on any vehicle that will require CNG fuel tank venting. Open the manual lock-down screws located on the HPL manual shut-off fittings by rotating the Allen screw counterclockwise until fully seated on vehicles that does not require venting of CNG fuel tanks. If service requires that the ignition be turned ON with CNG components or lines disconnected, keep the ALT FUELS fuse removed to prevent CNG fuel venting during an ignition ON prime pulse.
NOTE:
If engine fails to operate on CNG or fails to start at all, go to step 5.
NOTE:
Dedicated alternative fuel vehicles (RPO KL8) have a third mid-frame mounted fuel tank that must also be manually closed.