JLG Articulating Boom Lift 9 Fault Code: Coolant Temperature
Coolant Temperature · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
Fault code 9 on a JLG articulating boom lift points to a problem in the coolant temperature sensor circuit, identified as SPN 110 with FMI 2. This means the controller sees an erratic, invalid, or out-of-range signal from the sensor, most often caused by a short circuit or a broken cable, and has disabled the related monitoring function until the fault is fixed.
Medium severity. This is a sensor circuit fault, not an actual overheating event. The engine can still run, but the coolant temperature monitoring function is disabled, meaning a real overheat condition could go undetected until the sensor issue is resolved.
What does JLG Articulating Boom Lift error code 9 mean?
Fault code 9 is tied to the coolant temperature sensor circuit, logged under SPN 110 with an FMI 2 designation. FMI 2 generally points to a signal that is erratic, intermittent, or otherwise invalid, rather than simply reading too high or too low.
This code falls under the sensor fault group. The controller has identified a wiring or component issue at the coolant temperature sensor, such as a short circuit or a cable break, rather than an actual coolant temperature problem.
Because the sensor's signal cannot be trusted, the machine's coolant temperature monitoring function tied to this sensor is deactivated. That means the operator loses the benefit of automatic overheat detection or warning tied to this circuit until the fault is corrected.
Common causes of 9
- Short circuit in the coolant temperature sensor's wiring or connector.
- Cable break (open circuit) somewhere between the sensor and the controller.
- Failed or degraded coolant temperature sensor itself.
How to troubleshoot JLG Articulating Boom Lift 9: first checks
- Check the sensor cable for visible damage, chafing, pinches, or corrosion at the connector.
- Check the sensor itself and replace it if it tests bad or shows physical damage.
- Check the fault limits programmed for the sensor to confirm they match the expected range for the sensor installed.
- Inspect the wiring harness routing near the engine for heat damage or contact with moving parts, since coolant sensor wiring often runs close to the engine block.
How the code clears
No separate clearing step is listed. Once the sensor cable, sensor, and fault limits have been checked and any faulty component repaired or replaced, the fault should clear on its own as the controller reads a valid signal again. No reset procedure is listed for this code.
Frequently asked questions
What does JLG fault code 9 mean?
It means the controller detected a fault in the coolant temperature sensor circuit, logged as SPN 110 with FMI 2. This points to a wiring or sensor problem, such as a short circuit or broken cable, not necessarily an actual overheating condition.
Is it safe to keep operating the machine with fault code 9 active?
The machine may still run, but the coolant temperature monitoring function tied to this sensor is disabled while the fault is active. That means an actual overheat condition could go unnoticed. It is best to diagnose and repair the sensor circuit as soon as practical rather than ignoring the code.
What causes fault code 9 on a JLG boom lift?
The most common causes are a short circuit or a cable break in the coolant temperature sensor's wiring, or a failed sensor itself.
How do I troubleshoot fault code 9?
Start by checking the sensor cable for damage or corrosion, then check the sensor and replace it if needed, and finally verify the fault limits programmed for that sensor match what is expected for the installed component.
Does fault code 9 require a special reset procedure?
No reset procedure is listed for this code. Once the wiring or sensor issue is repaired, the fault should clear when the controller sees a valid signal again.
Why does the controller disable monitoring when this fault is active?
Because the sensor's signal cannot be trusted while it is shorted or broken, the controller deactivates the associated monitoring function rather than relying on bad data, which could otherwise trigger false readings or mask a real problem.