JLG Telescopic Boom Lift 33 Fault Code: Driver Problem
Also called Contactor Coil is Short-Circuited, Driver is Short-Circuit, Engine Coolant Temperature (EOT) Sensor High Voltage
Driver Problem · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
Fault 33 on JLG telescopic boom lifts (E600 and related platforms) most commonly flags a main dump output short to battery, though the same numbered slot is also used across different control modules for contactor coil short-circuits and other output driver faults. It is a priority 6 communicated fault, meaning it shows up on the analyzer and points to a wiring or driver problem, not normal operation.
Medium severity. Priority 6 faults are communicated to the analyzer and generally do not shut the machine down outright, but a shorted main dump circuit or contactor coil can disable a key hydraulic function or drive contactor, so it should be diagnosed before continued operation.
What does JLG Telescopic Boom Lift error code 33 mean?
Fault code 33 is not a single fixed fault across every JLG control system. Depending on which fault table the machine's controller uses, position 33 in the communicated fault list can mean 'main dump short to battery,' or on other control boards it maps to 'short-circuit reverse contactor coil.' Both point to the same underlying problem type: an electrical output driver or contactor coil that is seeing a short-circuit condition rather than the normal on/off switching the controller expects.
The main dump valve controls hydraulic pressure relief in the lift or drive circuit, so a short to battery on that output means the controller is sensing voltage on the circuit when it should be reading it as off, or the driver itself has failed. A shorted contactor coil means the coil is drawing excess current, so the controller's coil overcurrent protection prevents it from energizing the forward, reverse, or line contactor when commanded.
All these faults are communicated (displayed on the analyzer) faults at priority 6, meaning the controller logs and displays them for the technician rather than immediately disabling all machine functions, but the affected circuit will not function correctly until the fault is cleared.
Common causes of 33
- Main dump valve output wiring shorted to the battery positive circuit, causing the controller to detect short to battery on that driver
- Forward, reverse, or line contactor coil shorted internally, tripping the controller's coil overcurrent protection
- Damaged or chafed wiring harness allowing the main dump or contactor coil circuit to contact a battery-voltage wire
- Failed output driver inside the control module itself, not the field wiring
- Water intrusion or corrosion at connectors feeding the main dump valve or contactor coil creating an unintended short path
How to troubleshoot JLG Telescopic Boom Lift 33: first checks
- Check the main dump valve wiring harness for chafing, pinches, or contact with battery-voltage wiring, especially near frame pass-throughs
- Inspect the forward, reverse, and line contactor coils for visible damage, and measure coil resistance to check for an internal short
- Look for corrosion or moisture at connectors on the main dump circuit and at contactor coil connections
- Disconnect the suspect valve or contactor coil and check whether the fault clears on the analyzer, which helps isolate wiring versus component versus controller driver
- Confirm which control module and fault table the machine uses, since fault 33 maps differently depending on the module, and cross check the analyzer's exact fault description text against the wiring diagram for that circuit
How the code clears
No separate clearing step is listed for fault 33. Once the short to battery condition on the main dump circuit, or the shorted contactor coil, is repaired, the fault should stop being reported on the analyzer during normal operation. Cycling the key or running the machine's self test after repair is good practice to confirm the fault does not recur.
Affected models and serial ranges
33 appears in our records across 1 JLG Telescopic Boom Lift models. Match your machine by model and serial number.
| Model | Serial ranges |
|---|---|
| E600 | Serial range not listed in source records |
Frequently asked questions
What does JLG fault code 33 mean?
On most JLG telescopic boom lift control systems, fault 33 in the communicated fault list is 'main dump short to battery,' meaning the controller detected battery voltage on the main dump valve output circuit when it should have read as off. On some other control modules, the same numbered position is used for a short-circuit reverse contactor coil fault. Check which description your analyzer displays to know which condition applies to your machine.
Is fault code 33 an emergency stop condition?
No. It is listed as a priority 6 communicated fault, meaning it is displayed on the analyzer for the technician rather than forcing an immediate machine shutdown. However, the affected circuit, whether it's the main dump valve or a drive contactor, will not work correctly until the fault is fixed, so it should not be ignored.
Can I keep operating the lift with fault 33 active?
It depends on which function is affected. If the main dump valve or a drive contactor is not operating correctly, hydraulic or drive functions tied to that circuit may not behave as expected. It is safest to have the fault diagnosed and repaired before continuing normal operation.
What usually causes a main dump short to battery fault?
The most common cause is chafed or damaged wiring that lets the main dump circuit contact a battery-voltage wire, though a failed output driver inside the controller can cause the same fault without any wiring damage.
Why does fault 33 sometimes show a contactor coil description instead of main dump?
Different JLG control modules use different fault numbering tables. On some boards, position 33 corresponds to main dump short to battery, while on others it is assigned to short-circuit reverse contactor coil. Always match the fault number to the exact description shown on your machine's analyzer.
Is there a reset procedure for fault 33?
No reset procedure is listed for this code. Repairing the underlying wiring or component short is what stops the fault from being reported.
Does fault 33 affect all JLG telescopic boom lift models the same way?
The E600 and related models covered by these fault tables share similar fault structures, but the exact fault list position and wording can differ between chassis module configurations, so always confirm against the specific fault description text on the analyzer.