JLG Telescopic Boom Lift 31 Fault Code: Contactor Did Not Close When Energized
Also called Contactor did not Close when Energized, Contractor Did Not Close When Energized, Coolant Temperature Warning, Fuel Pump Low Voltage, Help Comment - Fuel Level Low - Engine Shutdown
Contactor Did Not Close When Energized · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
Fault code 31 on JLG telescopic boom lifts (flash code 3-1) most commonly means a line or direction contactor failed to close when the controller energized it. On some E600 engine setups the same numeric code area is tied to a coolant temperature warning (SPN 110 / FMI 0). Both readings point to problems that can stall drive function or overheat the engine, so treat the code as a stop-and-check condition.
High severity. A contactor that will not close can leave the machine without reliable traction control, and a coolant temperature warning left unaddressed can lead to engine overheating damage. Neither condition should be driven through or ignored.
What does JLG Telescopic Boom Lift error code 31 mean?
Flash code 3-1 on JLG lifts is described as a contactor that did not close when the controller sent it power. Contactors are the heavy relays that switch battery or motor power to the traction and direction circuits, so if one fails to close, the drive system may not respond correctly, or at all, in one or both directions.
On machines with the SPN 110 / FMI 0 designation, the same fault code space is used for a coolant temperature warning. This means coolant temperature has exceeded a warning level, and a fault message will show until temperature drops back below a recovery level. The system may also apply a delay time-fill limitation while this condition is active.
There is also a fuel pump low voltage description and a fuel level low engine shutdown help comment tied to this code group, though no further numeric detail is given for those conditions.
Common causes of 31
- Line and direction contactor coils miswired, so that closing the line contactor makes traction point A go high without the capacitor bank charge rising to battery supply, typically from coil wiring being swapped between the line and a direction contactor
- Open circuit in the forward direction contactor or traction motor, where traction point A does not go high when the forward contactor is energized, due to an open traction motor winding or a power wiring error
- Open circuit in the line contactor itself, where capacitor bank charge does not rise to battery supply when the line contactor is energized, due to a power wiring error
- Open circuit in the reverse direction contactor or traction motor, where traction point A does not go high when the reverse contactor is energized, due to an open traction motor winding or a power wiring error
- Coolant temperature exceeding the warning level on affected engine setups
- Fuel pump low voltage condition, or fuel level low leading to an engine shutdown help comment
How to troubleshoot JLG Telescopic Boom Lift 31: first checks
- Check wiring at the line and direction contactor coils for swapped connections; confirm each coil is wired to its correct contactor position
- Inspect the line contactor and its power wiring for open circuits or loose/corroded connections that would prevent capacitor bank charge from rising to battery supply
- Check the traction motor windings and power wiring for open circuits in both the forward and reverse directions
- Check engine coolant level and condition, and inspect the coolant temperature sensor and its cable for damage or poor connection
- Check fuel level and fuel pump voltage if a low voltage or low fuel condition is suspected
- Select the specific engine model from the controller or service tool list for further code detail, since this code varies by engine
How the code clears
For the coolant temperature warning, the fault message clears on its own once coolant temperature drops back below the recovery level; a delay time-fill limitation may apply after the warning. For the contactor-related flash code 3-1, no separate reset procedure is listed. Correct the wiring, contactor, or motor fault and confirm normal contactor operation before returning the machine to service.
Affected models and serial ranges
31 appears in our records across 1 JLG Telescopic Boom Lift models. Match your machine by model and serial number.
| Model | Serial ranges |
|---|---|
| E600 | Serial range not listed in source records |
Frequently asked questions
What does JLG fault code 31 mean?
It most often means a line or direction contactor did not close when the controller energized it, shown as flash code 3-1. On some E600 engine configurations the same code area, SPN 110 / FMI 0, is used for a coolant temperature warning instead.
Is fault code 31 the same as SPN 110 / FMI 0?
On certain engine setups, yes. SPN 110 / FMI 0 is listed as a coolant temperature warning under this code group, separate from the contactor-related flash code 3-1 description used elsewhere.
Can I keep operating the lift with fault code 31 active?
It is not recommended. A contactor that fails to close can affect drive direction control, and an active coolant temperature warning signals the engine is running hotter than intended. Stop and diagnose before continuing work.
Why would the contactor not close when energized?
Listed causes include miswired line and direction contactor coils, an open circuit in the forward or reverse direction contactor or traction motor, or an open circuit in the line contactor itself, often from a power wiring error.
Does the coolant warning clear itself?
Yes. The fault message disappears once coolant temperature drops back below the recovery level, though a delay time-fill limitation may apply afterward.
What should I check first for a coolant temperature warning on this code?
Check the coolant level and condition first, then inspect the coolant temperature sensor and its cable for damage, corrosion, or a loose connection.
Is fuel pump voltage related to this fault code?
A fuel pump low voltage description and a fuel level low engine shutdown help comment are both grouped under this code, though no specific voltage or level threshold is given.