JLG Articulating Boom Lift 353 Fault Code: Megajector Delivery Pressure Higher Than Expected
Megajector Delivery Pressure Higher Than Expected · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
Fault code 353 sets when the megajector's actual fuel pressure reading differs from its commanded pressure by more than 4.00 inches (10.1 cm) of H2O. It points to a fuel delivery problem on LPG-fueled engines, most often fuel supply pressure, a leaking lockoff solenoid, a bad reference line, regulator icing, or a cooling system issue. If none of those check out, the megajector itself has failed internally.
Medium severity. This code does not describe an immediate structural or lifting hazard, but it affects engine fuel delivery on an LPG-fueled machine. Diagnose before continued use since running with unstable fuel delivery pressure can cause poor engine performance or stalling in the field.
What does JLG Articulating Boom Lift error code 353 mean?
Fault code 353 is set by the machine's engine control system when it detects that the megajector's actual delivery pressure does not match what it commanded, with a gap larger than 4.00 inches (10.1 cm) of H2O.
The megajector is the electronically controlled fuel metering device on LPG-fueled JLG boom lifts. It regulates how much fuel vapor is delivered to the engine based on commanded pressure. When the actual pressure reading runs higher than expected compared to command, the controller flags this code to warn that something downstream or upstream of the megajector is affecting fuel delivery.
This is fundamentally a fuel system diagnostic code. It can be caused by a supply-side pressure problem, a sealing issue in the lockoff solenoid, a blocked or damaged reference line, ice buildup on the regulator, a cooling system fault, or, if all else checks out, a failed megajector unit itself.
Common causes of 353
- Fuel supply pressure at the megajector inlet fitting outside the expected range for LPG applications, which should read between 3-5 inches (7.6-12.7 cm) H2O.
- Lockoff solenoid not sealing completely when closed, allowing pressure creep in the fuel system.
- Reference line between the megajector and the carburetor balance port missing, kinked, restricted, or holed, disrupting the pressure reference signal.
- Regulator icing up due to a cooling system problem, preventing proper vaporization and pressure regulation.
- Engine cooling system not operating properly, including air locks in the system or the engine not reaching proper operating temperature, which can cause the regulator to ice.
- Internal failure of the megajector itself if all of the above check out normal.
How to troubleshoot JLG Articulating Boom Lift 353: 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 for LPG applications.
- Inspect the lockoff solenoid to confirm it seals fully when closed, with no pressure creep past it.
- Trace the reference line from the megajector to the carburetor balance port. Confirm it is properly connected, not kinked, not restricted, and free of holes.
- With the engine running, observe the regulator for signs of icing. If icing is present, move to checking the cooling system.
- Verify the engine cooling system is working properly with no air locks. Confirm the engine reaches proper operating temperature and that both coolant hoses at the regulator feel warm, confirming coolant is circulating through it.
- If fuel supply, lockoff, reference line, regulator, and cooling system all check out normal, the megajector likely has an internal failure and needs to be replaced.
How the code clears
No separate clearing step is listed for this code. Once the underlying fuel delivery issue is corrected, whether that is fuel supply pressure, the lockoff solenoid, the reference line, regulator icing, or the cooling system, the code should stop resetting on its own. If the megajector is replaced due to internal failure, that also resolves the fault.
Frequently asked questions
What does JLG fault code 353 mean?
It means the machine's controller detected that the megajector's actual fuel delivery pressure was higher than commanded by more than 4.00 inches (10.1 cm) of H2O. It is a fuel system fault tied to the LPG megajector unit.
What should fuel supply pressure read on an LPG machine with code 353?
Fuel supply pressure at the megajector inlet fitting should read between 3-5 inches (7.6-12.7 cm) H2O. If it's outside that range, that is a likely cause of the fault.
Can a bad reference line cause code 353?
Yes. The reference line runs between the megajector and the carburetor balance port. If it's disconnected, kinked, restricted, or has a hole in it, the megajector cannot read pressure correctly, which can trigger this code.
Why would the regulator be icing up?
Regulator icing usually points to an engine cooling system problem. Check for air locks in the cooling system, confirm the engine reaches proper operating temperature, and check that both coolant hoses at the regulator are warm to verify coolant is circulating.
Does code 353 always mean the megajector needs to be replaced?
Not always. Replacement is only needed if fuel supply pressure, the lockoff solenoid, the reference line, and the cooling system all check out fine. If everything else is normal, the megajector has an internal failure and must be replaced.
Is it safe to keep operating the lift with code 353 active?
It's best to diagnose the fault before continued use. Unstable fuel delivery pressure on an LPG engine can lead to poor performance or stalling, which is not something you want happening mid-shift or while working at height.