JLG Scissor Lift 311 Fault Code: Open Circuit Line Contactor
Open Circuit Line Contactor · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
Code 311 on JLG M3369 and M4069 scissor lifts means the power module's line contactor did not close when the controller energized it. Help text confirms: Line contactor did not close. With this fault active, drive, steer, and lift up are all prevented.
High severity. The machine will not drive, steer, or lift while this code is active. It is not a hidden hazard, but it is a full functional stop until the contactor circuit is repaired.
What does JLG Scissor Lift error code 311 mean?
Code 311 means the power module tried to close the main line contactor and it did not respond. The line contactor is the big relay-like switch that connects battery power to the drive system. If it will not close, the controller locks out drive, steer, and lift up functions because it cannot verify that power is flowing correctly to those systems.
This is a protective response. Rather than let the machine attempt to move or lift without a confirmed, closed power path, the controller shuts those functions down until the contactor issue is resolved.
Common causes of 311
- Open or damaged wiring between the contactor main contacts and the battery positive terminal or the power controller B+ terminal
- Failed or out-of-spec contactor solenoid coil (should measure about 52 ohms)
- Open or damaged wiring between the contactor solenoid and the power module 12-position connector terminal 8, or the ground board terminal J1-19
- Faulty line contactor that fails to close even when properly energized
How to troubleshoot JLG Scissor Lift 311: first checks
- Inspect and test the contactor main contact wiring run from the battery positive terminal to the power controller B+ terminal for looseness, corrosion, or an open connection
- Measure the contactor solenoid coil resistance and confirm it reads about 52 ohms; replace the contactor if it is significantly off from this
- Check the solenoid wiring between the power module 12-position connector terminal 8 and ground board terminal J1-19 for continuity and damage
- With the machine attempting to close the contactor, check whether power module 12-position connector terminal 8 drops from 24 volts away to almost nothing; if it does, the signal is good and the contactor itself should be replaced
- If wiring and solenoid resistance check out but the contactor still will not close, replace the line contactor
How the code clears
No separate clearing step is listed. Repair follows the check sequence: confirm main contact wiring, verify solenoid resistance, check solenoid control wiring to the power module and ground board, verify the terminal 8 voltage transition during a contactor close attempt, and replace the contactor if the wiring and signal are good but it still fails to close.
Affected models and serial ranges
311 appears in our records across 2 JLG Scissor Lift models. Match your machine by model and serial number.
| Model | Serial ranges |
|---|---|
| M3369 | Serial range not listed in source records |
| M4069 | Serial range not listed in source records |
Frequently asked questions
What does JLG fault code 311 mean?
It means the line contactor in the power module did not close when the controller tried to energize it. This is an open circuit line contactor fault, and it blocks drive, steer, and lift up functions until it clears.
Why can't I drive or lift with code 311 active?
The line contactor is the main power switch feeding the drive system. If the controller cannot confirm it closed properly, it will not allow drive, steer, or lift up, since those functions depend on a verified power path.
What resistance should the contactor solenoid read?
The contactor solenoid should measure about 52 ohms. A reading well outside that range points to a failed coil and a contactor that needs replacing.
How do I know if the contactor itself is bad versus a wiring problem?
Check power module 12-position connector terminal 8 while the machine attempts to close the contactor. If that terminal transitions from 24 volts down to almost nothing, the control signal is working correctly and the contactor itself should be replaced.
Which JLG scissor lift models use this code?
Fault code 311 for open circuit line contactor is documented on the JLG M3369 and M4069 models.
Is code 311 safe to ignore or work around?
No. It is a functional lockout, not a nuisance code. Drive, steer, and lift up are disabled by design until the contactor circuit is repaired, so the machine should not be forced into operation.