JLG Scissor Lift 93 Fault Code: Stack Overflow
Also called Indicates Controller (Module) Problems - LSS Has Not Been Calibrated, LSS Has Not Been Calibrated
Stack Overflow · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
Fault code 93 (SPN / FMI 2) on JLG scissor lifts points to two distinct issues depending on machine setup: the load sensing system (LSS) has not been calibrated after configuration, or in some controllers, an internal program logic fault described as a stack overflow. Either version can shut the machine down or block engine start until addressed.
High severity. This code can trigger an emergency switch-off and prevent the engine from starting. The lift may also be treated as overloaded by the controller until the load sensing system is properly calibrated, so operators should not try to work around the fault.
What does JLG Scissor Lift error code 93 mean?
Fault code 93 covers two different root situations reported under the same flash code. The first is that the load sensing system's calibration EEPROM for empty platform load was set at the factory to never set, a signature put in by the in-circuit test fixture during manufacturing, combined with the machine setup being configured for CUTOUT PLT or CUTOUT ALL load cutout modes. Because the calibration was never actually performed on the real machine, the controller assumes the vehicle is overloaded and won't clear this fault until a valid calibration overwrites that EEPROM value.
The second reported cause is an internal calculation fault inside the controller logic itself, referred to as a stack overflow. This is a program logic issue rather than a sensor or wiring problem. When it occurs, the controller records it as an emergency switch-off condition and the engine cannot be started until it is addressed.
In both cases the fault is tied to the load sensing system: either it is configured but never calibrated, or the controller's internal processing tied to that logic has faulted. Either way, treat the lift as unsafe to operate until the fault is resolved.
Common causes of 93
- Load sensing system calibration EEPROM for empty platform load was left at its factory default (never-set) signature applied by the in-circuit test fixture, while machine setup is configured for CUTOUT PLT or CUTOUT ALL load cutout mode.
- The controller assumes the vehicle is overloaded because no valid empty-platform calibration has ever been written to the load sensing system.
- Internal controller calculation fault, described as a stack overflow, within the program logic.
- LSS reported as configured in the machine setup but not yet calibrated (reported by the analyzer at priority level noted internally by JLG diagnostics).
How to troubleshoot JLG Scissor Lift 93: first checks
- Confirm whether the machine's load cutout setting is CUTOUT PLT or CUTOUT ALL, since this combination with an uncalibrated LSS is a known trigger for this code.
- Check whether the load sensing system has ever been calibrated on this specific machine versus just configured in setup.
- Cycle the ignition off and on, then recheck for the fault. This is the documented first step for the stack overflow variant.
- If the fault returns after a power cycle, treat it as a controller logic fault rather than a calibration issue and contact JLG service rather than attempting further field diagnosis.
- Inspect for any recent controller replacement or reflash, since an in-circuit test fixture signature left in place is a common cause after component swaps.
How the code clears
For the LSS-not-calibrated cause, run the manufacturer's load sensing system calibration procedure. Once a valid calibration is written, it overwrites the factory test-fixture signature in the EEPROM and clears the fault. For the stack overflow / internal calculation fault variant, switch the ignition off and back on, then check again. If the fault persists after that cycle, JLG service should be contacted, since this points to an internal controller logic problem rather than something field-adjustable.
Frequently asked questions
What does JLG fault code 93 mean?
It means the load sensing system (LSS) is configured but has not been calibrated, or in some controllers, an internal program logic fault called a stack overflow has occurred. Both are reported under fault code 93, SPN with FMI 2.
Why won't my JLG scissor lift start with fault code 93 active?
If the cause is the internal calculation (stack overflow) fault, the controller treats it as an emergency switch-off condition and blocks engine start entirely. If the cause is an uncalibrated load sensing system combined with a CUTOUT PLT or CUTOUT ALL setting, the machine may also refuse normal operation because it assumes the platform is overloaded.
How do I clear fault code 93 on a JLG scissor lift?
If it is the calibration issue, run the load sensing system calibration procedure so a valid calibration overwrites the factory test signature. If it is the stack overflow variant, cycle the ignition off and on and check again. If it comes back, contact JLG service.
Can I just recalibrate the load sensing system myself to fix this?
Yes, if the cause is the uncalibrated LSS combined with a CUTOUT PLT or CUTOUT ALL setup. Running the proper calibration procedure is the documented fix. It will not help if the actual cause is the internal stack overflow logic fault.
Is fault code 93 safe to ignore or work around?
No. The fault can trigger an emergency switch-off and prevent engine start, and if it's the load sensing calibration issue, the machine may be assuming an overload condition. Continuing to operate around this fault risks both equipment damage and operator safety.
What is a stack overflow fault on a JLG controller?
It's described as an internal calculation fault within the controller's program logic, not something caused by wiring, sensors, or operator input. It results in an emergency switch-off and blocks engine starting until cleared or repaired.