JLG Articulating Boom Lift 23 Fault Code: Problems with Boom Function Selection
Also called Foot Switch Selected Before Start, Hand Throttle High Voltage, Lift/Swing Joystick Center Tap Bad, Lift/Swing Joystick Out of Range High, Lift/Swing Joystick Out of Range Low, Lift/Swing Locked - Joystick Moved Before Foot Switch, Not Used, Pump Switches Faulty - Check Diagnostics/Boom, Pump Switches Locked - Selected Before Aux Power, Pump Switches Locked - Selected Before Foot Switch, Pump Switches Locked - Selected Before Start Switch, Start Switch Locked - Selected Before Key Switch
Problems with Boom Function Selection · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
Fault code 23 on JLG articulating boom lifts covers a group of related faults tied to the lift/swing joystick, pump/boom function switches, and start sequence interlocks. It sets when a boom function switch or joystick is activated out of the correct sequence (before start switch, foot switch, or aux power), when both directions of a function are selected together, or when joystick signal voltages fall outside their valid range. Priority is listed as (3).
Medium severity. Code 23 is priority (3), which is not an engine-shutdown level fault, but it will lock out lift, swing, or boom functions until the interlock condition or sensor fault is cleared. Operators should treat it as a stop-and-diagnose condition before resuming platform work.
What does JLG Articulating Boom Lift error code 23 mean?
Fault code 23 is a shared code covering several distinct diagnostic messages related to the lift/swing joystick circuit and the boom function (pump) switches on JLG articulating boom lifts. The controller uses this code to flag either an out-of-sequence operator input or a joystick signal that is out of its expected voltage range.
Several of the listed conditions are sequence lockouts: the machine detected a boom function switch, joystick movement, or pump switch closed before the start switch, key switch, foot switch, or auxiliary power was activated in the proper order. These are safety interlocks meant to prevent unexpected boom or swing movement during startup.
Other conditions under this code point to joystick hardware or wiring problems: the center tap voltage on the lift/swing joystick reading outside its valid band, the joystick signal being out of range high or low, or (on inductive joystick machines) the qprox sensor reading incorrectly or showing no activation when the joystick is moved. On some control systems, a faulty pump pot will force all platform boom functions except upper lift and swing to run at creep speed only.
Common causes of 23
- Platform upper lift or swing joystick was moved before or during foot switch closure (lift/swing locked - joystick moved before foot switch/EMS/FSW).
- A boom function (lower lift, telescope, basket level, basket rotate, or jib) had both directions selected at the same time (pump switches faulty).
- A platform boom function switch was closed before the key switch or foot switch closed (pump switches locked - selected before foot switch).
- A ground-mode boom function switch was selected before auxiliary power was applied, or before the key switch on some systems (pump switches locked - selected before aux power).
- A hydraulic function switch was closed before the start switch was closed (pump switches locked - selected before start switch).
- The operator attempted to start the machine with the foot switch already engaged (foot switch selected before start).
- On inductive joystick machines, the joystick was moved out of neutral with no qprox sensor active, or the qprox sensor read above 3.18 volts (qprox bad).
- Lift/swing joystick out of range high or low: on inductive joysticks this is tied to the centertap voltage; on resistive joysticks the out-of-range-low fault does not occur, and out-of-range-high only occurs if Vref is above 7.7 volts (out of tolerance or a short to battery), since it does not occur below 8.1 volts.
- Lift/swing joystick center tap voltage out of its valid band: on resistive joysticks this is outside 3.08 volts to 3.83 volts (with a possible 0.1 volt tolerance band), and on inductive joysticks it is outside 2.18 volts to 2.70 volts (with a similar 0.1 volt tolerance band).
- The lift/swing or swing/lift joystick center tap is out of valid range or the wiper circuit is wire-off (lift/swing joystick faulty / swing/lift joystick faulty).
- The pump pot circuit is open, which forces all platform boom functions except upper lift and swing into creep speed only (pump pot faulty).
How to troubleshoot JLG Articulating Boom Lift 23: first checks
- Confirm the correct startup sequence was followed: key switch, then start switch, then foot switch, without touching the joystick or any boom function switch out of order. Many of these faults clear simply by restarting in the correct sequence.
- Check that no boom function switch is stuck or wired so that both directions can close at once (lower lift, telescope, basket level, basket rotate, jib). Inspect the switch and its wiring for damage or contamination.
- With the key on and machine safe to test, check the lift/swing joystick center tap voltage against the valid range for the joystick type (resistive or inductive) fitted to the machine, and compare against 3.08 to 3.83 volts (resistive) or 2.18 to 2.70 volts (inductive).
- On inductive joystick machines, check the qprox sensor output. It should not read above 3.18 volts, and it should show activity when the joystick is moved out of neutral.
- Inspect the joystick wiring harness and connectors for corrosion, chafing, or a wire-off condition on the wiper circuit, especially if the fault text specifies center tap or wiper faults.
- On resistive joystick machines, verify Vref is within tolerance; the out-of-range-high fault relates to Vref above 7.7 volts, indicating out-of-tolerance Vref or a possible short to battery.
- If platform boom functions other than upper lift and swing are limited to creep speed only, suspect an open-circuit pump pot and check that circuit for continuity.
How the code clears
No separate clearing step is listed for this code beyond correcting the condition that triggered it. Since most of the listed faults are sequence-based interlocks (switch, joystick, or pump switch activated in the wrong order relative to start, foot switch, or aux power), cycling the key switch and restarting the machine in the correct sequence, without pre-engaging any joystick or function switch, is expected to clear the fault. For voltage-range or wiring faults, correcting the underlying wiring, connector, or sensor problem is needed before the fault will stay clear.
Frequently asked questions
What does JLG fault code 23 mean?
It is a grouped fault code covering several conditions tied to the lift/swing joystick and boom function pump switches. It can mean an operator activated a joystick or switch out of the correct startup sequence, selected both directions of a boom function at once, or that a joystick signal (center tap, qprox, or range) is out of its valid voltage window.
Why does my JLG boom lift show fault 23 every time I start it?
This usually points to a sequence problem: the foot switch, a boom function switch, or the joystick was engaged before the correct startup step (key switch, start switch, foot switch, or aux power). Make sure nothing is touching the joystick or function switches during startup and that the foot switch is not already pressed when you try to start.
Is fault code 23 dangerous to keep operating with?
It is priority (3), not an engine-stopping fault, but it locks out the affected lift, swing, or boom function as a safety interlock. You should not try to work around it. Diagnose and clear the actual cause before resuming platform operation.
What voltage should the lift/swing joystick center tap read?
On resistive joysticks it should read between 3.08 volts and 3.83 volts. On inductive joysticks it should read between 2.18 volts and 2.70 volts. A small 0.1 volt tolerance band applies to both due to resistor tolerances.
Why are my boom functions running only at creep speed?
On some control systems this points to a faulty pump pot. If that circuit is open, all platform boom functions except upper lift and swing are forced to run at creep speed only until the pump pot circuit is repaired.
Does fault code 23 apply differently to inductive versus resistive joysticks?
Yes. Several of the sub-faults, like qprox faults and out-of-range-low, only occur on inductive joysticks. Out-of-range-low does not occur at all on resistive joysticks, and out-of-range-high on resistive joysticks depends on the Vref voltage rather than a centertap reading.
How do I clear fault code 23 after fixing the problem?
No separate clearing procedure is listed. For sequence-related faults, cycling the key switch and restarting in the correct order typically clears it. For wiring or sensor faults, the fault should clear once the wiring, connector, or joystick issue is physically repaired.