JLG Boom Lift 33 Fault Code: Contactor Coil is Short-Circuited
Contactor Coil is Short-Circuited · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
JLG fault code 33 on the M600 boom lift means the controller detected a short circuit in a contactor coil, either the forward, line, or reverse contactor, or found an overloaded valve supply circuit drawing current with no valve energized. The machine's ground module wiring is the most likely culprit.
High severity. This code stops normal drive or lift function because the affected contactor cannot be safely energized. Continued operation risks further electrical damage to the controller or wiring, so the machine should be diagnosed before returning to service.
What does JLG Boom Lift error code 33 mean?
Fault code 33 covers a group of related electrical faults tied to the contactor coils that control forward, reverse, and line (main power) functions on the M600 boom lift. Contactors are heavy-duty relays that switch high current to the drive and lift circuits. Each coil has over-current protection built into the controller logic. When that protection trips, the controller logs code 33 and the contactor stays de-energized to prevent damage.
One cause listed under this code is not a coil short at all but an overloaded valve supply: the controller sees a high current draw on the valve supply circuit even though no valve is commanded on. This points to a wiring fault at the ground module rather than the contactors themselves.
In short, code 33 tells you a coil circuit (forward, line, or reverse) or the valve supply wiring is pulling more current than it should, and the controller has shut that circuit down as a protective measure.
Common causes of 33
- Wiring error at the ground module causing a high current draw on the valve supply circuit when no valve is energized (overloaded valve supply)
- Short circuit in the forward contactor coil, preventing the forward contactor from energizing when required due to coil over-current protection
- Short circuit in the line contactor coil, preventing the line contactor from energizing when required due to coil over-current protection
- Short circuit in the reverse contactor coil, preventing the reverse contactor from energizing when required due to coil over-current protection
How to troubleshoot JLG Boom Lift 33: first checks
- Inspect wiring at the ground module for damage, chafing, pinched wires, or incorrect connections that could cause a high current draw on the valve supply circuit
- Check the forward, line, and reverse contactor coils for signs of shorting: melted insulation, discoloration, or a burnt smell
- Test each contactor coil's resistance and continuity to ground to identify which coil is shorted
- Check wiring harnesses and connectors leading to each contactor for pinched, chafed, or corroded wiring that could cause a short to ground or to another circuit
- Verify connectors at the ground module are fully seated and free of corrosion before replacing any components
How the code clears
No reset procedure is listed for this code. Once the wiring fault or shorted coil is found and repaired, the controller should stop logging the fault on the next power cycle, but the code should be verified as cleared by cycling power and testing forward, reverse, and line contactor operation.
Affected models and serial ranges
33 appears in our records across 1 JLG Boom Lift models. Match your machine by model and serial number.
| Model | Serial ranges |
|---|---|
| M600 | Serial range not listed in source records |
Frequently asked questions
What does JLG fault code 33 mean on an M600 boom lift?
It means the controller detected a short circuit in one of the contactor coils (forward, line, or reverse) or found an overloaded valve supply circuit drawing current with no valve energized. It is an electrical fault tied to coil over-current protection.
Can I keep operating the boom lift with fault code 33 active?
It is not recommended. The affected contactor will not energize when needed, which can disable forward, reverse, or main power drive functions. Continuing to operate risks further electrical damage.
Which contactor is causing my code 33?
Code 33 can be triggered by the forward, line, or reverse contactor coil, or by a wiring fault at the ground module affecting the valve supply. You need to check each coil individually to isolate which one is shorted.
What is the ground module and why does it matter for this fault?
The ground module is tied to the valve supply wiring. A wiring error there can cause a high current draw even when no valve is commanded on, which the controller flags under fault code 33.
Is there a reset procedure for fault code 33?
No reset procedure is listed for this code. Repair the underlying wiring or coil fault first, then cycle power and confirm the contactors operate correctly.
What parts should I inspect first if I get code 33?
Start with the wiring at the ground module, then check the forward, line, and reverse contactor coils for shorting, and inspect all related harnesses and connectors for chafing or corrosion.