JLG Articulating Boom Lift 354 Fault Code: Megajector Delivery Pressure Lower Than Expected
Megajector Delivery Pressure Lower Than Expected · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
Fault code 354 sets on JLG articulating boom lifts when the megajector's actual delivery pressure drops more than -4.00 inches (10.1 cm) of H2O below the commanded pressure. This points to a fuel delivery problem on LPG-fueled units, usually low supply pressure, a restricted hose, a lockoff solenoid not fully opening, a blocked reference line, or a regulator icing up due to a cooling system issue.
Medium severity. This code affects engine fuel delivery, not a safety interlock or lifting function directly. However, an engine running lean or losing power unexpectedly during boom operation is a real operational hazard, so it should be diagnosed before continued use rather than ignored.
What does JLG Articulating Boom Lift error code 354 mean?
Code 354 is about the megajector, which regulates LPG fuel delivery to the engine. The controller compares the pressure it commanded from the megajector against the pressure it actually measures. If the actual pressure comes in more than -4.00 inches (10.1 cm) of H2O below what was commanded, the system flags this fault.
In plain terms, the engine is asking for a certain amount of fuel pressure and not getting it. That mismatch can come from anywhere in the fuel delivery path: the supply itself, the hoses carrying fuel, the lockoff solenoid that gates fuel flow, the reference line that lets the regulator sense engine vacuum, or icing in the regulator caused by a cooling system that isn't keeping it warm enough.
Because this is a fuel delivery fault on an LPG engine, it can cause rough running, stalling, loss of power, or a no-start/no-run condition depending on how severe the pressure shortfall is.
Common causes of 354
- Low fuel supply pressure at the megajector inlet fitting, outside the normal LPG range of 3-5 inches (7.6-12.7 cm) H2O
- Fuel system hoses that are kinked, pinched, cut, loose, or not clamped tight
- Lockoff solenoid not opening completely, restricting fuel flow
- Reference line between the megajector and carburetor balance port missing, kinked, restricted, or holed
- Regulator icing up during operation
- Engine cooling system not operating properly, including air locks or coolant not circulating to the regulator, causing the regulator to run cold and ice
How to troubleshoot JLG Articulating Boom Lift 354: first checks
- Check fuel supply pressure at the megajector inlet fitting and confirm it falls between 3-5 inches (7.6-12.7 cm) H2O
- Inspect all fuel system hoses for kinks, pinches, cuts, or loose clamps and make sure they are clamped tight and in good condition
- Verify the lockoff solenoid opens fully when commanded; a solenoid that only partially opens will starve the system of fuel
- Confirm the reference line between the megajector and the carburetor balance port is connected, unkinked, unrestricted, and free of holes
- With the engine running, observe the regulator for signs of icing
- Check the coolant hoses at the regulator to make sure both are warm, which confirms proper coolant circulation and rules out an air lock or cooling system fault
How the code clears
No separate clearing step is listed for this code. Diagnosis focuses on fixing the underlying fuel supply, hose, lockoff, reference line, or cooling issue causing the pressure shortfall; once the megajector's actual pressure tracks the commanded pressure within range, the fault should not re-trigger. If the fault persists after these checks, further inspection of the megajector and its wiring or connectors may be needed.
Frequently asked questions
What does JLG fault code 354 mean?
It means the megajector's actual fuel delivery pressure is reading more than -4.00 inches (10.1 cm) of H2O lower than what the controller commanded, indicating a fuel delivery restriction or supply problem on the LPG system.
What is the normal fuel supply pressure for LPG on these machines?
Fuel supply pressure at the megajector inlet fitting should be between 3-5 inches (7.6-12.7 cm) H2O on LPG applications. Anything outside that range should be investigated as a likely cause of code 354.
Can a bad lockoff solenoid cause this fault?
Yes. If the lockoff solenoid does not open completely, it restricts fuel flow and can cause low fuel pressure, which triggers this code.
Why would the regulator be icing up?
Regulator icing usually points back to the engine cooling system. If coolant isn't circulating properly to the regulator, or there's an air lock in the system, the regulator can run too cold and ice up, disrupting fuel delivery.
Is this fault dangerous to keep operating with?
It's not a lifting or structural safety fault, but it affects engine fuel delivery. Running with degraded fuel pressure can cause stalling or power loss, which is a real hazard if it happens while the machine is in use. It should be diagnosed promptly rather than run through a full shift.
What should I check first if I get code 354?
Start with fuel supply pressure at the megajector inlet, then inspect the fuel hoses, lockoff solenoid operation, the reference line to the carburetor balance port, and finally the cooling system and coolant hoses at the regulator for icing.
Does this code apply to diesel or gasoline JLG models?
No, this fault is specific to the megajector fuel delivery system used on LPG-fueled applications. Diesel and gasoline fuel systems don't use a megajector in this configuration.