Fuel System Pressure Release

Connect scan tool to communicate with Alternative Fuel Engine Control Module (AF ECM). Store Diagnostic Trouble Code (DTC) information. Clear DTC information and turn ignition off. Start and idle engine. Ensure engine is running on CNG by observing that Fuel Indicator Light (FIL) is off. Using scan tool, select high-pressure lock-off relay function. Command lock-off relay OFF and observe fuel tank pressure sensor data. When engine stalls or switch-over to gasoline occurs, turn ignition off and remove CNG 20-amp fuse. A small amount of CNG will remain in lines. Slowly loosen fitting to release existing line pressure.