JLG Scissor Lift 663 Fault Code: CAN Bus Failure - Load Sensing System Module
Also called Communications - CAN Bus Failure - Load Sensing System Module
CAN Bus Failure - Load Sensing System Module · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
Code 663 sets when the platform station is active, the platform option is enabled, a platform is detected as attached, the load sensing menu is configured to something other than none, and the UGM cannot detect the load sensing system (LSS) module on the CAN bus. The machine treats this as a communications failure and locks out lift, telescope, rotate, and level functions until the machine is power cycled.
High severity. The machine disables lift up/down, telescope in/out, platform rotate, and platform level functions and shows a platform overloaded screen. It stays locked out until a power cycle, so the platform is effectively unusable until the fault is fixed.
What does JLG Scissor Lift error code 663 mean?
Code 663 means the control system, specifically the UGM, is not receiving CAN bus messages from the load sensing system module even though the load sensing menu is configured to expect it. The load sensing system is responsible for telling the machine whether the platform is overloaded, and if that link goes quiet, the controller assumes it cannot trust the load data.
Because the controller can't verify platform load, it shuts down the functions that could get the machine into trouble: lift up, lift down, telescope in, telescope out, platform rotate left and right, and platform level up and down. It also disables the platform module output at J2-19 (the function enable relay) and tells the LCD to display a platform overloaded screen, even though the real issue is a communications dropout, not necessarily an actual overload.
The controller also disregards any CAN messages that come in with platform module source addresses while this fault is active, since it no longer trusts that channel of the network.
What triggers a JLG Scissor Lift 663 code?
The fault sets when all of the following are true: the platform station is active, the platform option is configured as enabled, a platform is detected as attached, the load sensing menu screen is not configured as none, and the UGM does not detect the LSS module on the CAN bus. The fault latches until a power cycle.
Common causes of 663
- A wiring or connector problem between the load sensing system module and the CAN bus, preventing the UGM from seeing its messages.
- Loss of power to the load sensing system module. The module needs 24 volts between connector J1-1 and J1-2 to operate.
- Incorrect machine setup parameters (model number, market, or load settings) that cause the control system to expect a load sensing configuration that doesn't match the actual hardware.
- A failed or unresponsive load sensing system module itself.
- An underlying platform module communication fault. If DTC 662 is also present, that points to a broader platform module CAN issue that should be resolved first.
How to troubleshoot JLG Scissor Lift 663: first checks
- Confirm the platform station is active and a platform is actually attached, since the fault only sets under those conditions.
- In the analyzer, check MACHINE SETUP → MODEL NUMBER, MARKET, and LOAD settings are all correct for the machine as built.
- Check for 24 volts between load sense system module connector J1-1 and J1-2 to confirm the module has power.
- Turn the machine on in platform mode and check whether DTC 662 is also active. If it is, troubleshoot 662 first since it likely affects 663.
- Inspect the CAN bus wiring and connectors between the load sensing system module and the rest of the network for damage, corrosion, or loose pins.
- Verify the load sensing menu screen setting is correct for the machine, since a mismatch between configuration and actual hardware can trigger the fault even with good wiring.
How the code clears
This fault latches until a power cycle. After confirming and correcting the wiring, power supply, module, or setup issue, cycle machine power to clear the fault. No separate clearing step is listed beyond the power cycle.
Frequently asked questions
What does JLG fault code 663 mean?
It means the control system's UGM expected to communicate with the load sensing system module over the CAN bus but never heard from it, while the platform is active and load sensing is configured as required. The machine locks out lift, telescope, rotate, and level functions until power is cycled.
Why does the platform show 'overloaded' when code 663 sets?
The controller can't verify actual platform load because it lost communication with the load sensing module, so it defaults to showing a platform overloaded screen and disabling motion functions as a precaution, even if the platform isn't actually overloaded.
How do I clear fault code 663 on a JLG scissor lift?
Fix the underlying cause, whether that's a wiring issue, a power problem at the load sensing module, or a machine setup mismatch, then power cycle the machine. The fault is latched until a power cycle, so simply retrying the function will not clear it.
Should I check for other fault codes if I see 663?
Yes. Check specifically for DTC 662. JLG's own troubleshooting steps say if 662 is present, you should resolve that fault before continuing to chase 663, since it likely relates to a broader platform module communication issue.
What voltage should the load sensing module be getting?
You should measure 24 volts between load sense system module connector J1-1 and J1-2. If that voltage is missing or low, the module can't function and won't communicate on the CAN bus.
Can incorrect machine setup cause code 663?
Yes. Incorrect MODEL NUMBER, MARKET, or LOAD settings in the analyzer's MACHINE SETUP menu can cause a mismatch between what the control system expects and what's actually installed, which can trigger this fault.
Is it safe to keep operating the platform with code 663 active?
No. The machine itself disables lift up/down, telescope in/out, rotate, and level functions when this fault is active, so normal platform operation isn't possible until the fault is diagnosed and cleared.