JLG Scissor Lift 31 Fault Code: Coolant Temperature Warning
Also called Contactor Did Not Close When Energized, Fuel Pump Low Voltage, Indicates That a Contactor Did Not Close When Energized - Contactor Driver Permanently Off, Indicates That a Contactor Did Not Close When Energized - Open Circuit Line Contactor
Coolant Temperature Warning · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
Code 31 (SPN 110 / FMI 0) on JLG scissor lifts covers several related faults depending on the control system: a line contactor that failed to close when energized, a contactor driver stuck permanently off, an open-circuit line contactor, or a coolant temperature warning on machines with an engine. In most electrical variants, drive, steer, and lift up are prevented until the fault clears.
High severity. This code stops normal machine function in its electrical forms (drive, steer, and lift up prevented) and can indicate wiring or contactor failure. The coolant temperature variant is a warning that can lead to engine damage if ignored, so treat any version of code 31 as needing prompt attention rather than something to run through a shift.
What does JLG Scissor Lift error code 31 mean?
Code 31 is used across several JLG scissor lift control systems for related but distinct problems. On electric-drive machines with a power module, it most often means the line contactor, the switch that connects battery power to the drive system, did not close when the controller commanded it to energize. This can show up as a general 'contactor did not close' fault, a 'contactor driver 1 permanently off' fault, or an open-circuit line contactor fault where the capacitor bank charge did not rise to battery supply level when the contactor closed.
When this fault is active, the power module logic prevents drive, steer, and lift up as a protective measure, since the machine cannot safely confirm power is properly connected to the drive circuit.
On machines with an engine and coolant system, code 31 can instead represent a coolant temperature warning, meaning the engine coolant has exceeded its warning temperature level. This is a functional warning rather than a contactor fault, and it clears once coolant temperature drops back below the recovery level after a delay.
Common causes of 31
- Line contactor drive circuitry passed power-up self-tests but the contactor did not close when energized
- Power module reports a 'contactor did not close' fault (fault code 15d)
- Power module's line contactor drive circuitry failed to energize during power-up self-tests, reporting 'contactor driver 1 permanently off' (fault code 22d)
- Open-circuit line contactor: capacitor bank charge did not rise to battery supply voltage when the line contactor was energized, possibly due to a power wiring error
- Engine coolant temperature has exceeded its warning level
How to troubleshoot JLG Scissor Lift 31: first checks
- Check all power wiring connections to the line contactor for looseness, corrosion, or damage, especially if an open-circuit contactor condition is suspected
- Inspect the contactor itself for signs of sticking, pitting, or mechanical failure to close
- Check coolant level and condition if the machine has an engine and the fault relates to coolant temperature
- Check the coolant temperature sensor and its cable for damage or poor connection
- Refer to CANbus documentation for the power module message and status to identify which specific contactor sub-fault is active
How the code clears
No separate clearing step is listed for the contactor faults beyond correcting the underlying wiring, contactor, or power module issue. For the coolant temperature warning, the fault message clears on its own once coolant temperature drops back below the recovery level, subject to a delay time-fill limitation.
Frequently asked questions
What does JLG fault code 31 mean?
It depends on the machine's control system. On electric-drive scissor lifts it usually means the line contactor did not close when the power module tried to energize it, or the contactor driver circuit failed to energize at all. On machines with an engine, it can instead mean the engine coolant temperature has exceeded its warning level.
Can I still drive or raise the platform with code 31 active?
If the fault is a contactor-related version, drive, steer, and lift up are prevented until the issue is resolved. This is a built-in protection since the controller cannot confirm safe power delivery to the drive system.
What is an 'open-circuit line contactor' fault?
This means the capacitor bank charge did not rise to battery supply voltage when the line contactor was energized. It can be caused by a power wiring error and should be checked at the wiring and contactor connections.
Does code 31 always mean a contactor problem?
No. On machines with an engine and coolant system, code 31 can represent a coolant temperature warning instead of a contactor issue. Check coolant level, the coolant temperature sensor, and its cable if this applies to your machine.
Will the coolant temperature warning clear itself?
Yes. The fault message disappears once coolant temperature drops back below the recovery level, after a delay time-fill limitation. No manual reset is listed for this version.
How do I tell which version of code 31 I have?
Check the power module message and status through the CANbus documentation for your specific machine, since the code covers multiple distinct fault conditions including contactor failures and coolant warnings.