Caution: LPG is extremely cold, so protect your skin and eyes.
After the pressure has been released, fully couple the connector to the tank. You will want to try and start the truck before re-pressurizing the system, and when it starts open the tank valve fully. As an alternate solution, you could open the tank valve after setting the key to the run position. The key indicator of a faulty LP lock-off, is when this valve needs to open before it sees pressure, in order for the truck to start. At this point try to start the truck. If the truck starts and runs, then the LPG lock off solenoid located on top of the EPR, has failed. The lock off solenoid will need to be replaced if this occurs.
Credit and thanks to TMHNA Technical Services.