JLG Articulating Boom Lift 86 Fault Code: Internal Temperature
Also called Axle Extend Short to Battery or Open Circuit, Axle Extend Short to Ground, Axle Retract Short to Battery or Open Circuit, Axle Retract Short to Ground, Engine Shutdown - Axle Lockout Valve Fault, Front Left Wheel Blocked, Front Left Wheel Sensor Fault - Check Mounting, Front Left Wheel Sensor Out of Range High, Front Left Wheel Sensor Out of Range Low, Front Right Wheel Blocked, Front Right Wheel Sensor Fault - Check Mounting, Front Right Wheel Sensor Out of Range High, Front Right Wheel Sensor Out of Range Low, Left Front Steer Left Short to Battery or Open Circuit, Left Front Steer Left Short to Ground, Left Front Steer Right Short to Battery or Open Circuit, Left Front Steer Right Short to Ground, Left Rear Steer Left Short to Battery or Open Circuit, Left Rear Steer Left Short to Ground, Left Rear Steer Right Short to Battery or Open Circuit, Left Rear Steer Right Short to Ground, Problems with the Steering System, Rear Left Wheel Blocked, Rear Left Wheel Sensor Fault - Check Mounting, Rear Left Wheel Sensor Out of Range High, Rear Left Wheel Sensor Out of Range Low, Rear Right Wheel Blocked, Rear Right Wheel Sensor Fault - Check Mounting, Rear Right Wheel Sensor Out of Range High, Rear Right Wheel Sensor Out of Range Low, Restricted to Transport - Oscillating Axle Pressure Switch Disagreement, Right Front Steer Left Short to Battery or Open Circuit, Right Front Steer Left Short to Ground, Right Front Steer Right Short to Battery or Open Circuit, Right Front Steer Right Short to Ground, Right Rear Steer Left Short to Battery or Open Circuit, Right Rear Steer Left Short to Ground, Right Rear Steer Right Short to Battery or Open Circuit, Right Rear Steer Right Short to Ground
Internal Temperature · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
Fault 86 on JLG articulating boom lifts (SPN 171 / FMI 12) covers a wide group of axle oscillation, axle lockout, and steering valve or sensor problems. It can mean a short to battery, open circuit, or short to ground on an axle or steer valve, a steering angle sensor out of range or decoupled, a blocked wheel, or a disagreement at the oscillating axle lockout pressure switch. Depending on which specific condition triggers it, the machine may restrict drive, steer, or lift functions, or prevent engine starting entirely.
High severity. This code covers many distinct faults, some of which stop the engine or block drive, steer, and lift functions until the condition clears or the machine goes through an EMS cycle. Because engine shutdown and function lockout are both possible outcomes, treat any code 86 as high priority until you identify which specific condition triggered it.
What does JLG Articulating Boom Lift error code 86 mean?
Fault 86 is a grouped fault code (SPN 171 / FMI 12) that JLG uses for a whole family of axle and steering related problems on articulating boom lifts equipped with oscillating axles and multi-wheel steering. Rather than pointing to one wire or one part, it can represent any of nearly 40 distinct conditions, from a shorted steer valve to a steering angle sensor that has come loose from its mount.
Most of these conditions fall into three groups: the axle extend/retract valve circuits (shorts to battery, open circuit, or shorts to ground), the steer valve circuits on all four corners (right front, left front, right rear, left rear, each with left and right steer solenoids), and the steering angle sensors and wheel-blocked logic that tell the controller whether a wheel is actually turning the way it was commanded.
A separate but related condition involves the oscillating axle lockout valve and its pressure switch. The controller expects pressure at this switch only when the lockout solenoid is energized for transport driving. If pressure shows up when it should not, or is missing when it should be there, the machine can restrict drive, steer, and lift functions, and in some cases will shut down or block engine starting altogether.
What triggers a JLG Articulating Boom Lift 86 code?
The oscillating axle lockout pressure switch disagreement must be detected for at least 5 seconds to set the fault, and it is ignored if engine speed is under 1200 RPM. For a blocked front right wheel, the controller commands steering for at least 1.3 seconds without seeing an appropriate angle change from the sensor before flagging the wheel as blocked. Steering angle mechanical limits also factor into blocked-wheel logic: with the axle fully retracted, steering is mechanically limited to about 25 degrees, and as the axle extends this limit increases to about 45 degrees, though the control system holds the machine to 25 degrees until the axle is fully extended.
Common causes of 86
- Short to battery or open circuit on the axle extend or retract valve, or on any of the eight steer valve solenoids (right front, left front, right rear, left rear steer left/right)
- Short to ground on the axle extend or retract valve or any steer valve solenoid
- Steering angle sensor decoupled from its mounting on any wheel (front left, front right, rear left, rear right)
- Steering angle sensor out of range low (short to ground or open circuit) or out of range high (short to battery)
- A wheel not responding to steer commands within the expected time, logged as a blocked wheel condition
- Oscillating axle lockout pressure switch indicating pressure when the lockout solenoid is not energized, or not indicating pressure when it is energized
- Mechanical blockage or hydraulic problem preventing a wheel from steering as commanded
How to troubleshoot JLG Articulating Boom Lift 86: first checks
- Check the diagnostic display or analyzer for the specific text description tied to this fault occurrence, since code 86 covers many distinct conditions and the exact wording tells you which circuit or sensor is involved
- Inspect wiring and connectors at the axle extend/retract valve and all steer valve solenoids for corrosion, chafing, or loose pins, especially if the fault text mentions a short to battery, open circuit, or short to ground
- Check the mounting of the steering angle sensor on the affected wheel corner, looking for a sensor that has come loose or shifted, which can cause both the decoupled fault and out-of-range readings
- Look for physical or hydraulic obstructions preventing a wheel from steering, particularly if the fault text says a wheel is blocked
- Verify the oscillating axle lockout valve solenoid and its pressure switch operate together correctly, confirming pressure is only present when the solenoid is energized for transport driving
- Confirm engine RPM and transport position status if the fault involves the oscillating axle lockout system, since this fault is ignored below 1200 RPM and ties directly into transport position logic
How the code clears
No single reset procedure applies to all conditions under fault 86. The blocked wheel conditions are stated to clear automatically when the underlying condition clears. The oscillating axle lockout pressure switch disagreement fault remains active until an EMS cycle. For the related condition where a short to battery or open circuit is detected on the axle lockout valve along with pressure indicated while out of transport position, engine starting is prevented and the operator must use auxiliary power to lower the boom to transport position before the machine can be restarted.
Frequently asked questions
What does JLG fault code 86 mean?
It is a grouped fault (SPN 171 / FMI 12) covering axle extend/retract valve faults, steer valve faults on all four wheel corners, steering angle sensor faults, blocked wheel conditions, and oscillating axle lockout pressure switch disagreements. The exact meaning depends on which specific fault text is shown on the display.
Why won't my JLG boom lift start after code 86 appears?
If the fault involves a short to battery or open circuit on the axle lockout valve along with pressure indicated while the boom is out of transport position, the controller prevents engine starting. You need to use auxiliary power to lower the boom to transport position before the engine can be restarted.
Why is my machine restricted to transport position?
This happens when the oscillating axle lockout pressure switch disagrees with the expected state of the lockout solenoid, meaning it shows pressure when it shouldn't or doesn't show pressure when it should. Drive, steer, tower lift up, main lift up, and main telescope out are all prevented until this clears.
What does a blocked wheel fault mean?
It means the controller commanded a steering change but did not see the expected angle response from that wheel's steering angle sensor within the expected time, at least 1.3 seconds for the front right wheel example given. This can come from a mechanical blockage, a hydraulic problem, or a faulty sensor. The fault clears automatically once the condition clears.
Does engine RPM affect this fault?
Yes, for the oscillating axle lockout pressure switch condition specifically. That fault is ignored if engine speed is under 1200 RPM, and the pressure disagreement must persist for at least 5 seconds before it sets.
Can a loose sensor mount cause code 86?
Yes. If a steering angle sensor becomes decoupled from its mounting on any of the four wheel corners, the controller flags a fault indicating the sensor should be checked for proper mounting.
Is code 86 safe to keep driving with?
No. Depending on the specific condition, this fault can restrict or fully disable drive, steer, and lift functions, and in some cases prevents the engine from starting at all. Treat it as a stop-and-diagnose situation rather than something to work around.