JLG Scissor Lift 91 Fault Code: Fuel Pump Low Voltage
Also called Indicates Controller (Module) Problems - LSS Watchdog Reset, LSS Watchdog Reset
Fuel Pump Low Voltage · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
Fault code 91 (SPN 94 / FMI 4) on JLG scissor lifts is reported when the load sensing system (LSS) module's microprocessor watchdog timer has been triggered, causing a watchdog reset. It also appears in relation to 'Fuel Pump Low Voltage' descriptions in the fault list, but the core condition tracked by this flash code is the LSS watchdog reset event. When active with machine setup load set to CUTOUT PLT or CUTOUT ALL, motion interlocks are disabled until power is cycled.
Medium severity. This code does not by itself indicate a load or hydraulic failure, but it can disable motion interlocks depending on machine setup, so the platform may lose expected safety cutout behavior until power is cycled and the fault clears.
What does JLG Scissor Lift error code 91 mean?
Fault code 91 is triggered when the watchdog timer inside the load sensing system (LSS) module's microprocessor resets. A watchdog timer is a safety check built into the module: if the processor doesn't respond or 'check in' within its expected cycle, the watchdog assumes something went wrong and forces a reset of the module.
This reset can happen because of electrical noise interference reaching the module, or because of an actual hardware problem inside the module itself. Either way, the module reports this event as a status message (0x81) showing 'watchdog rst.'
If the machine's load setup is configured to CUTOUT PLT (platform cutout) or CUTOUT ALL, this fault condition is retained and motion interlocks tied to the load sensing system are affected, meaning normal interlock behavior may not apply until the fault is cleared by cycling power.
What triggers a JLG Scissor Lift 91 code?
The code is set when the LSS module's status message (0x81) reports a 'watchdog rst' event, combined with the machine setup's load parameter being configured to 1 (CUTOUT PLT) or 2 (CUTOUT ALL). The fault is retained until power to the machine is recycled.
Common causes of 91
- Excessive electrical noise reaching the load sensing system module's microprocessor, disrupting normal processor operation and triggering the watchdog timer.
- A hardware difficulty within the LSS module itself, causing the microprocessor to stop responding as expected and forcing a watchdog reset.
- Machine setup configured with load cutout set to CUTOUT PLT or CUTOUT ALL, which causes the watchdog reset condition to be retained and to affect motion interlocks until power is cycled.
How to troubleshoot JLG Scissor Lift 91: first checks
- Inspect wiring and connectors around the LSS module for loose connections, corrosion, or damage that could allow electrical noise into the circuit.
- Check for nearby sources of electrical interference or poor grounding that could affect the module's microprocessor.
- Verify the machine setup's load cutout parameter (CUTOUT PLT or CUTOUT ALL) to understand whether motion interlocks are currently affected by this fault.
- Cycle power to the machine to see if the fault clears, since this is the documented step to clear a retained watchdog reset.
How the code clears
Recycle power to the machine to clear the difficulty. No further reset procedure is listed for this code. If the fault returns immediately after a power cycle, treat it as a sign of a genuine hardware problem in the LSS module rather than a one-time noise event.
Frequently asked questions
What does JLG fault code 91 mean?
It means the load sensing system (LSS) module's microprocessor watchdog timer was triggered and the module reset itself. This is logged as a 'watchdog rst' status message.
Is fault code 91 the same as SPN 94 FMI 4?
Yes, fault code 91 corresponds to SPN 94 with FMI 4 in the diagnostic listing.
Will fault code 91 stop the scissor lift from moving?
It can affect motion interlocks if the machine setup's load parameter is set to CUTOUT PLT or CUTOUT ALL, since the fault condition is retained until power is cycled.
How do I clear JLG fault code 91?
Recycle power to the machine. This is the only resolve step documented for this fault.
What causes the LSS watchdog reset?
Either excessive electrical noise affecting the module's microprocessor, or an internal hardware problem with the LSS module.
Does fault code 91 always mean a hardware failure?
Not necessarily. Electrical noise can trigger the same watchdog reset as an actual hardware fault, so a power cycle and repeat check is the first step before assuming a module failure.