Onboard Charger Fault Detected During Charge Cycle

Common Symptoms

• Platform LCD on the upper control box displays code 24 during or after a charge cycle
• Battery charge indicator does not increase even after the machine sits plugged in overnight
• Machine operates sluggishly or loses drive power partway through a shift
• Onboard charger status light stays red or flashes an error pattern instead of turning green
• Machine powers on but platform functions cut out sooner than expected under normal loads
• Charger fan runs briefly then shuts off without completing a full charge cycle
• Alarm or fault light on the lower control box stays lit after plugging in AC power

Probable Causes (Ranked by Likelihood)

• AC input power problem at the charge outlet, such as a tripped GFCI, loose cord, or low facility voltage below the charger's input threshold Very Likely
• Onboard charger unit internal fault or failed charge module requiring replacement Likely
• Battery pack voltage too low (deeply discharged) for the charger to initiate a charge cycle, causing the charger to fault out immediately Likely
• Loose or corroded DC wiring between the charger output and the battery pack terminals Possible
• One or more battery cells shorted or open, presenting an abnormal load that causes the charger to fault Possible
• Charger sense or interlock wiring fault, such as a broken wire or corroded connector on the charger signal harness Less Likely
• Onboard charger overheating due to blocked ventilation or high ambient temperature, triggering the charger's thermal protection Less Likely

Step-by-Step Diagnostic Procedure

1. Check the AC power source first. Plug a known working tool or light into the same outlet to confirm you have live AC power. If a GFCI is present, press the RESET button and retry. Verify the extension cord or whip is fully seated at both ends and rated for the charger's input current.

2. Measure AC input voltage at the charger's plug with a multimeter. Most Skyjack onboard chargers require 110-120V AC within 10 percent of nominal. A reading below 100V or above 132V will cause a charger fault. If voltage is out of range, the facility supply is the problem, not the machine.

3. Inspect the charger DC output wiring. With AC power disconnected, check all cable connections between the charger output terminals and the battery pack for looseness, corrosion, or heat damage. Clean corroded terminals with a wire brush and re-torque to spec.

4. Check battery pack open-circuit DC voltage. Fully disconnected from the charger, measure across the battery pack terminals. A 24V system should read at least 20V and a 48V system at least 40V for the charger to start a normal cycle. A reading well below these values means the pack is deeply discharged. Some charger models have a recovery mode; consult the Skyjack service manual for your specific charger model. If the pack will not recover, the batteries may need replacement.

5. Inspect each battery for physical damage, swelling, or leaking electrolyte. A single bad battery in the series string can cause the charger to report a fault. Measure individual battery voltages to identify any cell reading significantly lower than the others.

6. Check the charger signal or interlock connector. Locate the small multi-pin connector on the charger harness and inspect for bent pins, water intrusion, or corrosion. Use dielectric grease on the connector after cleaning. A fault on this signal line can make the charger behave as though it is in a fault state even when the AC and DC circuits are healthy.

7. If all wiring and power checks are normal and the charger still displays a fault, the charger module itself is likely failed. Replacement of the onboard charger unit is an advanced step. Record the charger brand and model number printed on the charger label before ordering a replacement, as Skyjack uses multiple charger vendors across model years. Contact your Skyjack dealer or use the EZcal / Pcal handheld with the Skyjack diagnostic harness to read extended fault data before condemning the unit.

Frequently Asked Questions