JLG Telescopic Crawler Boom Lift 23 Fault Code: Problems with Boom Function Selection
Problems with Boom Function Selection · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
Fault code 23 on JLG telescopic crawler boom lifts covers a group of boom function selection faults, priority (3), that trigger when a joystick or hydraulic function switch is activated out of the correct sequence, both directions of a function are selected together, or a joystick/qprox sensor reads outside its expected voltage range. It is not a single failure but a family of related conditions, all tied to how and when the operator or ground control switches, joysticks, and foot switch are engaged.
Medium severity. Code 23 will not let a boom function operate until the fault condition clears, so it stops work but does not by itself indicate imminent mechanical damage. However, some sub-conditions point to wiring shorts or failed sensors that should not be ignored, since continued operation with a stuck or miswired joystick input creates a real control risk.
What does JLG Telescopic Crawler Boom Lift error code 23 mean?
Fault code 23 is a communicated, displayed fault covering problems with boom function selection on JLG telescopic crawler boom lifts. It has a priority of (3) and actually represents eleven distinct sub-conditions, all related to sequencing, dual-direction selection, or joystick/qprox sensor voltage readings that fall outside allowed limits.
At its core, this fault exists to stop the machine from acting on an ambiguous or unsafe operator input. If lift, swing, telescope, basket level, basket rotate, or jib functions are commanded before the foot switch, key switch, start switch, or aux power are properly engaged, or if a function is commanded in both directions at once, the controller does not know what the operator actually intends and locks out that function until the input is corrected.
Several of the sub-conditions are specific to inductive joysticks and their qprox sensors, which sense joystick position without physical contact. If these sensors are inactive, reading too high, or the centertap voltage is outside its expected window, the controller cannot trust the joystick signal and sets a fault rather than risk sending an unintended boom command.
Common causes of 23
- Operator moved the lift or swing joystick before or during foot switch closure instead of after.
- A boom function (lower lift, telescope, basket level, basket rotate, or jib) had both directions selected at the same time, pointing to a faulty or stuck pump switch.
- A platform boom function was selected before the key switch or foot switch was closed.
- A ground boom function was selected before auxiliary power was applied.
- Inductive joystick moved out of neutral with no qprox sensors active.
- Inductive joystick qprox sensor reading above 3.18 volts, indicating a bad qprox sensor.
- Inductive joystick signal below the calculated low threshold: below 1.05 volts if centertap is at the high end of its range, or below 0.79 volts if centertap is at the low end.
- Resistive joystick Vref voltage out of tolerance or shorted to battery, triggered when Vref is above 7.7 volts (faults for out-of-range-high do not occur if Vref stays below 8.1 volts).
- Inductive joystick signal above the calculated high threshold: above 4.35 volts if centertap is at the high end of its range, or above 3.8 volts if centertap is at the low end.
- Resistive joystick centertap voltage outside 3.08 volts to 3.83 volts, with a possible +/- 0.1 volt tolerance band around those limits.
- Inductive joystick centertap voltage outside 2.18 volts to 2.70 volts, with a possible +/- 0.1 volt tolerance band around those limits.
- A hydraulic function switch closed before the start switch was closed.
- Foot switch engaged while attempting to start the machine, instead of being released first.
How to troubleshoot JLG Telescopic Crawler Boom Lift 23: first checks
- Check the exact sequence of operation: release all joysticks and function switches to neutral, then engage the foot switch/key switch/start switch/aux power in the correct order before commanding a boom function.
- Inspect pump switches and hydraulic function switches for sticking, corrosion, or mechanical damage that could cause both directions of a function to read as selected at once.
- On machines with inductive joysticks, check qprox sensor wiring and connectors for corrosion, looseness, or damage, since a sensor reading above 3.18 volts or showing no active sensors will set this fault.
- Verify joystick centertap voltage with a meter: resistive joysticks should read between 3.08 volts and 3.83 volts, inductive joysticks should read between 2.18 volts and 2.70 volts, allowing for a +/- 0.1 volt tolerance.
- On resistive joysticks, check Vref supply voltage and confirm it stays below 8.1 volts; a reading above 7.7 volts points to an out-of-tolerance supply or a short to battery.
- Confirm the foot switch is fully released before attempting to start the machine, and check the foot switch circuit for a switch that is stuck closed or miswired.
- Cycle the joystick through its full range while monitoring signal voltage to see if it crosses the calculated out-of-range low or high thresholds tied to the centertap reading.
How the code clears
No separate clearing step is listed. Correcting the sequence of operation, such as releasing joysticks and switches to neutral and engaging the foot switch, key switch, start switch, or aux power in the proper order, should allow the fault to clear on its own. If the fault relates to a joystick or qprox sensor voltage reading, it will not clear until the underlying wiring, sensor, or switch problem is repaired and the readings return to the listed voltage ranges.
Frequently asked questions
What does JLG fault code 23 mean on a telescopic crawler boom lift?
It means the controller detected a problem with boom function selection. This covers several possible conditions, including moving a joystick or hydraulic switch before the foot switch, key switch, start switch, or aux power was engaged, selecting both directions of a function at once, or a joystick/qprox sensor voltage reading outside its allowed range.
Is fault code 23 caused by operator error or a hardware failure?
It can be either. Many of the eleven sub-conditions are triggered simply by operating switches or joysticks in the wrong sequence, which clears once the correct sequence is followed. Others point to a genuine hardware issue, such as a stuck pump switch, failed qprox sensor, or out-of-tolerance joystick voltage, which requires inspection and repair.
Why does my machine set fault code 23 only when I use certain joysticks?
Several sub-conditions apply only to inductive joysticks with qprox sensors, while others apply only to resistive joysticks. Inductive joysticks are checked against centertap-based voltage thresholds and qprox sensor activity, while resistive joysticks are checked against fixed centertap voltage ranges and Vref supply voltage.
What voltage should a joystick centertap read?
On resistive joysticks, centertap voltage should fall between 3.08 volts and 3.83 volts, with a possible +/- 0.1 volt tolerance. On inductive joysticks, it should fall between 2.18 volts and 2.70 volts, again with a possible +/- 0.1 volt tolerance. Readings outside these windows will set fault code 23.
Can I clear fault code 23 by just restarting the machine?
No separate clearing step is listed, so if the fault was caused by an operating sequence error, correcting that sequence, such as releasing the foot switch and joysticks before restarting, should let it clear. If it is caused by a wiring or sensor fault, it will likely return until that underlying problem is fixed.
Does fault code 23 stop the whole machine or just one function?
Based on the described conditions, it locks out the specific boom function involved, such as lift, swing, telescope, basket level, basket rotate, or jib, rather than shutting down the entire machine, though it will prevent that function from responding until the fault clears.
Should I keep operating the machine if fault code 23 keeps coming back?
No. A recurring fault code 23 suggests a wiring, switch, or sensor problem rather than a one-time sequencing mistake. Continued operation with an unreliable joystick or switch signal is a control risk, so the machine should be inspected and repaired before returning it to service.