JLG Power Module Failure Check Power Wiring Check Mosfet Short Circuit

Spoiler alert. If you don’t feel like reading what we had to do to fix the lift our problem was the brushes on the motor assembly. JLG part number 7027617. To save yourself about $400 you can purchase just the motor brushes for the JLG T350J and T500J here:

JLG T350J/T500J Motor Brushes (70003736) – Fixes 9 Flashes Error

Our JLG T500 manlift rental began giving our customers trouble on their jobsites. The symptoms of their problem was an occasional, not consistent, error resulting in 9 flashes on the JLG control panel. To be more specific, the error occurred only when the operator wanted to use these functions: lift up, jib up, telescope in and out, outriggers up or down. And to make matters even worse, the problem was only intermittent, meaning that sometimes the operator could get several minutes of use out of the lift before it failed again with 9-flashes. In every case the operator had to stop the machine and reset it before trying to use it again. The intermittency of the problem made troubleshooting very frustrating because sometimes the machine would work, and then it wouldn’t.

We hooked up our analyzer and it gave the following error message upon failure: “Power Module Failure – Check Power Wiring Check Mosfet Short Circuit (9/9)”. This diagnosis is better than the general error mentioned above, but it is still very vague. What it means is that there is a problem with the continuity of the 24V electrical circuit anywhere on the entire lift! And again, to make matters worse, our lift was losing electrical continuity only intermittently, or just enough to really frustrate our customer trying to get his work done. JLG lifts T350J and T500J require constant electrical continuity. Any time this continuity is broken the solenoid behind the batteries disengages and shuts down the machine. Only stopping and resetting the machine will re-energize the solenoid.

Searching the internet for “JLG Power Module Failure” or any combination of the title above revealed only a few results, and none of them were helpful to our intermittent situation. The suggestions we found on the internet recommended we check the batteries, the battery cables, and replace the power module. Luckily we have multiple lifts so we were able to swap all of the aforementioned. None of them solve the problem.

What the problem ended up being for us was the brushes inside the motor assembly located in the pump. Inside this container are four brushes that contact the motor shaft and spin it at 3300rpm. During this machine’s 250 hours of use the brushes inside the motor have worn. They haven’t worn completely enough to totally disable the machine, but only enough to give trouble intermittently. Due to the wear, but electrical continuity was sometimes present and other times not. This explains why every function that we used that required the motor to run is also the function that would intermittently disrupt the continuity and throw the machine into the 9-flashes shutdown.

We are not certified to give advice on fixing JLG lifts. We are only giving our account of what happened to us, and hopefully this will help someone else trying to fix their problem.