JLG Scissor Lift 99 Fault Code: LSS Needs to be Re-Calibrated
Also called EEPROM Failure - Check All Settings, Indicates Controller (Module) Problems - EEPROM Failure - Check All Settings, Indicates Controller (Module) Problems - Functions Locked Out - LSS Module Software Version Improper, Indicates Controller (Module) Problems - Functions Locked Out - Machine Not Configured, Indicates Controller (Module) Problems - Functions Locked Out - Platform Module Software Version Improper, Indicates Controller (Module) Problems - Functions Locked Out - Power Module Software Version Improper, Indicates Controller (Module) Problems - LSS Internal Error - DRDY Missing from A/D, Indicates Controller (Module) Problems - LSS Internal Error - Pin Excitation, Indicates Controller (Module) Problems - Power Module Failure - Check Power Circuits or MOSFET Short Circuit, Indicates Controller (Module) Problems - Power Module Failure - Internal Error, Indicates Controller (Module) Problems - Power Module Failure - Personality Range Error, Indicates Controller (Module) Problems - Power Module Failure - System Monitor, LSS Internal Error - DRDY Missing From A/D, LSS Internal Error - Driver Fault, LSS Internal Error - Pin Excitation, Problems with the Controller
LSS Needs to be Re-Calibrated · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
Code 99 on JLG scissor lifts (9-9 flash code) covers a group of controller and load sensing system faults, from EEPROM failure to power module self-test errors and software version mismatches. It generally locks out functions until the fault is corrected and power is recycled.
High severity. Code 99 locks out machine functions and can indicate real controller, wiring, or load sensing hardware problems. It should be diagnosed before returning the lift to service, since some causes point to the vehicle being assumed overloaded or to power module wiring faults that could recur.
What does JLG Scissor Lift error code 99 mean?
Fault code 99, shown as a 9-9 flash code on JLG scissor lifts, is an umbrella code for controller (module) problems. It can point to an EEPROM failure meaning settings should be checked, a power module failure, or a load sensing system (LSS) internal error. Because several distinct conditions share this code, the actual cause has to be narrowed down using the specific fault description or sub-code reported by the controller.
In most of these cases the control system locks out functions until the issue is corrected, and some faults are retained in memory until power is recycled. This means the lift may keep faulting even after the underlying wiring issue clears, until the controller is power cycled.
Some of the causes are tied to the load sensing system assuming the vehicle is overloaded, which is a safety-related lockout rather than a simple electronic glitch. Others point to a software version mismatch between the LSS module and the rest of the control system, or to an internal power module self-test failure.
Common causes of 99
- Power module detected an error in the power wiring for the drive or pump, or failed its own self-test.
- Power module reporting an armature MOSFET short circuit, or MOSFET's off, or MOSFET's on, or armature pullup MOSFET short circuit fault code, retained until power is recycled.
- Excitation voltage for the load sensors below 4.25V, reported by the LSS module status message (0x81) as an internal error, occurring when machine setup's load is set to CUTOUT PLT or CUTOUT ALL.
- DRDY interrupt from the load sensing system module's A/D converter missing, reported the same way through LSS status message (0x81) with load setup set to CUTOUT PLT or CUTOUT ALL.
- LSS module software major version not equal to version 7 while machine setup's LOAD is set to 1 or 2, making the control system incompatible and non-functional.
- Power module internal error detected via self-test, reporting a two direction fault, a sequence fault, a CAN bus input fault, a 12V supply detection fault, or a system monitor activated fault, retained until power is recycled.
How to troubleshoot JLG Scissor Lift 99: first checks
- Check the power module wiring to the drive motor and pump motor for damage, loose connections, or shorts.
- Inspect load sensor wiring for damage that could be excessively loading the excitation supply below 4.25V.
- Confirm the LSS module software major version installed is version 7.xx and compatible with the rest of the control system.
- Check machine setup parameters, specifically the LOAD setting (1=CUTOUT PLT or 2=CUTOUT ALL), to understand which fault path is active.
- Recycle power to the machine after inspection to see if the retained fault clears, since several of these faults are held in memory until a power cycle.
- Look for other flash codes accompanying the 9-9 code, such as MOSFET-related sub-codes, CAN bus input faults, or system monitor activation, to pin down the exact cause.
How the code clears
Most causes under code 99 require recycling power to the machine to clear the retained fault after the underlying issue is corrected. For software version mismatches, the fix is reprogramming or replacing the LSS module with a version 7.xx module. For wiring or hardware failures in the power module or load sensing system, the wiring must be repaired or the module replaced before the fault will stay clear. No separate clearing step is listed beyond these actions.
Frequently asked questions
What does JLG fault code 99 mean?
It's a general controller (module) problem code, shown as a 9-9 flash code, that can mean an EEPROM failure, a power module failure, a load sensing system internal error, or a software version mismatch. The exact cause depends on which sub-message the controller is reporting.
Why does my JLG scissor lift think it's overloaded when it isn't?
Two of the causes under code 99 involve the load sensing system reporting an internal error, either low excitation voltage below 4.25V or a missing DRDY interrupt from the A/D converter. In both cases the system assumes the vehicle is overloaded as a safety precaution, even if the real issue is wiring damage or a module hardware fault.
Will recycling power clear fault code 99?
Sometimes. Faults tied to power module wiring errors, MOSFET fault codes, and several internal power module self-test errors are retained until power is recycled. If the underlying wiring or hardware problem has been fixed, cycling power should clear the fault. If not, it will likely return.
What software version does the LSS module need?
The load sensing system module's software major version needs to equal version 7 when the machine's LOAD setup parameter is set to CUTOUT PLT or CUTOUT ALL. If the version doesn't match, the control system won't function properly and code 99 sets.
Can I keep operating the lift with code 99 active?
No. This code indicates functions are locked out until the difficulty is corrected. Operating with a controller or load sensing fault active risks incorrect load cutoffs or unpredictable drive and pump behavior.
Is fault code 99 an electrical or hydraulic problem?
It's primarily electrical, involving the power module's control of drive and pump wiring, MOSFET switching, and the load sensing system's sensor excitation circuits. It is not a hydraulic pressure fault.
What should a technician check first for code 99?
Start with the specific sub-fault reported, such as a MOSFET code, a CAN bus input fault, or an LSS internal error message, then inspect the related wiring, confirm the LSS module software version, and check the machine's LOAD setup parameter before recycling power.