JLG 800AJ: Boom will not raise or extend

Likely cause: Discharged battery, an active fault code, basket overload or a fault of the boom angle or length sensor. Diagnosis: Check the power supply, read the fault code and verify the load in the basket.

JLG 800AJ: Machine will not drive, or drives only at creep speed

Likely cause: Joystick out of range or not centred, an open footswitch, or the drive limitation that is active while the boom is raised. Diagnosis: Centre the joystick, check the footswitch and lower the boom to the stowed (transport) position.

JLG 800AJ: Tilt alarm

Likely cause: Working on a slope, or a damaged or uncalibrated tilt sensor. Diagnosis: Level the machine; calibration or replacement of the sensor at a service centre.

JLG 800AJ: Basket overload (overload / load sense)

Likely cause: Capacity exceeded or a basket load sensor out of calibration. Diagnosis: Reduce the load; calibration of the weighing system at a service centre.

JLG 800AJ: Boom sagging or descending slowly

Likely cause: Worn cylinder seals, a holding valve fault or air in the system; moisture can make valves stick. Diagnosis: Inspect the cylinders, valves and hydraulic oil; repair at a service centre.

JLG 800AJ: Loss of CAN communication between modules

Likely cause: Chafed bus cable, corroded connectors or a damaged module (basket, chassis, power module). Diagnosis: Check the bus and the connectors and read the fault code with a service analyser.

JLG 800AJ: Combustion engine: will not start, stalls, overheats

Likely cause: Glow plugs or relay, throttle position sensor (TPS), temperature and oil pressure sensors, fuel system. Diagnosis: Read the engine codes and check the sensors and wiring.

JLG 800AJ: Basket will not come down

Likely cause: No power to the lowering valves or an electrical fault. Diagnosis: Use the emergency lowering (the valve on the chassis), then have the electrics diagnosed at a service centre.

Faults and error codes · boom lift

JLG 800AJ service: faults and error codes

The most common faults of the JLG 800AJ (boom lift) with the likely cause and the way to diagnose them, and below the JLG error codes with explanations. RK Rental services the JLG 800AJ: repairs, maintenance inspections and preparation for UDT inspections (UDT is the Polish Office of Technical Inspection), parts and service life assessment.

JLG 800AJ: machine data

Type: boom lift
Working height: 26.38 m
Platform capacity: 230 kg
Drive: Diesel 4x4
Error codes in the database: 306

800AJ machine card →800AJ manuals and parts catalogue →JLG parts →

The information below is diagnostic and indicative. Repairs, calibrations and clearing of fault codes are carried out by a qualified service technician, according to the manual for the specific serial number of the machine. A machine with an active fault code must not be used until the cause has been removed.

JLG 800AJ technical data useful for service

Weight and dimensions decide how the machine is transported to a workshop, while the tyres, battery and drive decide which parts are needed. When you report a service job, please also give the serial number from the rating plate.

Outreach: 15.8 m
Machine weight: 15,757 kg
Platform dimensions: 1.83 × 0.91 m
Machine dimensions (L × W × H): 11.13×2.48×3 m

Most common JLG 800AJ faults

Boom will not raise or extend

Likely cause: Discharged battery, an active fault code, basket overload or a fault of the boom angle or length sensor.
Diagnosis / how to fix it: Check the power supply, read the fault code and verify the load in the basket.

Machine will not drive, or drives only at creep speed

Likely cause: Joystick out of range or not centred, an open footswitch, or the drive limitation that is active while the boom is raised.
Diagnosis / how to fix it: Centre the joystick, check the footswitch and lower the boom to the stowed (transport) position.

Tilt alarm

Likely cause: Working on a slope, or a damaged or uncalibrated tilt sensor.
Diagnosis / how to fix it: Level the machine; calibration or replacement of the sensor at a service centre.

Basket overload (overload / load sense)

Likely cause: Capacity exceeded or a basket load sensor out of calibration.
Diagnosis / how to fix it: Reduce the load; calibration of the weighing system at a service centre.

Boom sagging or descending slowly

Likely cause: Worn cylinder seals, a holding valve fault or air in the system; moisture can make valves stick.
Diagnosis / how to fix it: Inspect the cylinders, valves and hydraulic oil; repair at a service centre.

Loss of CAN communication between modules

Likely cause: Chafed bus cable, corroded connectors or a damaged module (basket, chassis, power module).
Diagnosis / how to fix it: Check the bus and the connectors and read the fault code with a service analyser.

Combustion engine: will not start, stalls, overheats

Likely cause: Glow plugs or relay, throttle position sensor (TPS), temperature and oil pressure sensors, fuel system.
Diagnosis / how to fix it: Read the engine codes and check the sensors and wiring.

Basket will not come down

Likely cause: No power to the lowering valves or an electrical fault.
Diagnosis / how to fix it: Use the emergency lowering (the valve on the chassis), then have the electrics diagnosed at a service centre.

JLG 800AJ error codes: 306 codes explained

JLG uses the JLG Control System. The flash code has the format group/subgroup (e.g. 2/1), and the full DTC is 3 to 5 digits (e.g. 255, 437, 662), read with a JLG analyser. The first digit indicates the system the fault relates to.

Below you see the code and the original manufacturer's message. Open a code for the likely cause, what you can check yourself and when to call service.

Source: JLG Service and Maintenance Manual: 600AJ (3121201), 800AJ (3120858), 460SJ, 860SJ, 1250AJP (3122581800), M450AJ (3121829), M600JP (3121711): Diagnostic Trouble Codes tables.

All JLG codes of this control system: list and search →

Do you have a fault or an error code on your JLG 800AJ?

Our service team will read the code, diagnose the cause and remove the fault, at our workshop or on site at the customer's premises (construction site, hall, warehouse), with original or OEM-grade replacement parts.

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Contact

The fastest way is by phone: service +48 609 609 105 (also WhatsApp), or write to serwis@fajnepodnosniki.pl.

Phone (service):: +48 609 609 105
E-mail:: serwis@fajnepodnosniki.pl
WhatsApp:: +48 609 609 105
Base and office:: ul. Brzozowa 12, 86-061 Brzoza near Bydgoszcz, Poland
Office hours:: Monday to Friday, 7:30–15:30 (Polish time)
Response time:: Messages: a reply within 1–2 hours.