JLG Boom Lift 14 Fault Code: Overcrank
Also called Engine Underspeed/Overcrank, Overcrank - 3 Failed Crank Cycles, Underspeed, Underspeed - Below 2000 RPM
Overcrank · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
Fault code 14 on JLG M600 boom lifts means the engine either failed to start after three failed crank cycles (overcrank) or dropped below 2000 RPM during running (underspeed). Either condition triggers an engine shutdown.
High severity. Code 14 causes a shutdown condition. The machine will not run the engine until the fault is resolved, and running the engine below the underspeed threshold or repeatedly failing to start can point to fuel delivery, air supply, or governor problems that need attention before continued use.
What does JLG Boom Lift error code 14 mean?
Fault code 14 covers two related engine problems on the JLG M600: overcrank, meaning the starter cranked the engine through three failed cycles without it starting, and underspeed, meaning the engine speed fell below 2000 RPM while running. Both conditions are treated the same way by the controller and both result in a shutdown.
This code is only active once a time delay bypass period has elapsed after engine startup, so it will not falsely trigger during the initial startup transient. Once that window passes, the controller watches for either failure to reach running speed or a drop below the underspeed threshold.
Because this is a shutdown-type fault, the practical effect is that the boom lift's engine stops running or will not start, which halts all lift and drive functions until the underlying fuel, air, or governor issue is fixed.
What triggers a JLG Boom Lift 14 code?
The fault is enabled once the time delay bypass period has elapsed after engine startup. It sets on overcrank after 3 failed crank cycles, or on underspeed when engine speed drops below 2000 RPM.
Common causes of 14
- Low fuel level or restricted fuel connections preventing adequate fuel delivery to the engine
- Fuel solenoid or fuel pump not operating correctly
- Weak or low start battery voltage affecting cranking speed
- Restricted combustion air supply, often from a dirty or clogged air cleaner
- Governor lever out of adjustment, affecting engine speed regulation
- Cold ambient temperature with a non-functioning heater or glow plug, preventing the engine from firing even though fuel is present
- Engine receiving fuel but not firing, indicated by white smoke in the exhaust during cranking
How to troubleshoot JLG Boom Lift 14: first checks
- Check the fuel level and inspect all fuel connections for leaks, air, or restrictions
- Verify the fuel solenoid and fuel pump are both operating as expected
- Check start battery voltage to confirm adequate cranking power
- Inspect the air cleaner and combustion air path for restrictions or blockage
- Verify the governor lever setting and re-adjust if it is out of specification
- In cold ambient conditions, confirm the heater and/or glow plug are functioning
- Watch the exhaust during a crank attempt: white smoke means fuel is reaching the engine but it is not firing, which points away from a fuel supply problem and toward an ignition or OEM-level engine issue
How the code clears
No separate clearing step is listed beyond correcting the underlying cause. Once fuel supply, air supply, battery voltage, governor setting, or cold-start assist issues are resolved, attempt a normal engine start. If the engine still overcranks or underspeeds after these checks, refer to the engine OEM for further diagnosis, since the fault may point to an internal engine issue beyond the boom lift's own fuel and air systems.
Affected models and serial ranges
14 appears in our records across 1 JLG Boom Lift models. Match your machine by model and serial number.
| Model | Serial ranges |
|---|---|
| M600 | Serial range not listed in source records |
Frequently asked questions
What does JLG fault code 14 mean on an M600 boom lift?
It means the engine either failed to start after 3 failed crank cycles (overcrank) or its speed dropped below 2000 RPM while running (underspeed). Both trigger an engine shutdown.
Why does my JLG boom lift shut down and show code 14 right after I try to start it?
This usually points to overcrank: the starter cranked the engine three times without success. Check fuel level, fuel connections, the fuel solenoid and pump, and start battery voltage first.
I see white smoke when cranking but the engine won't start. What does that mean?
White smoke during cranking means fuel is reaching the engine but it is not firing. This shifts the likely cause away from fuel supply and toward an ignition-related or engine-internal issue, so refer to the engine OEM for further checks.
Does cold weather affect code 14?
Yes. In low ambient temperatures, a heater or glow plug that is not working can prevent the engine from firing even with adequate fuel, triggering an overcrank shutdown. Verify these components are operating in cold conditions.
Can a dirty air cleaner cause fault code 14?
Yes. Restricted combustion air from a clogged air cleaner can prevent the engine from reaching or maintaining running speed, contributing to an underspeed condition.
Is fault code 14 dangerous to keep operating through?
It is a shutdown fault, so the machine will not continue running the engine through it. Attempting repeated crank cycles without addressing the root cause can drain the start battery and does not fix the underlying fuel, air, or governor problem.
When should I stop troubleshooting myself and call the engine OEM?
If you have checked fuel level and connections, fuel solenoid and pump operation, battery voltage, air cleaner condition, and governor lever setting, and the engine still overcranks or underspeeds, especially if white smoke is present, it is time to refer to the OEM for further diagnosis.