JLG 40HT Auxiliary Hydraulic Pump

Hi All,
I have an older JLG boom lift, model 40HT, that I am having issues with the electric auxiliary hydraulic system. All functions work fine with the gas engine running but with it turned off and the auxiliary pump toggled on I am unable to get any functions to work. I can hear the electric motor on the auxiliary pump running when toggled from either the basket or ground controls, but nothing will function from it. Any suggestions of where to start on further diagnosis would be greatly appreciated

Check the hydraulic pressure with your aux pump. It might be running at the motor but the pump might not be doing it’s thing.

Those aux. pumps do wear out. Especially if they were used a lot during the lift's working life. Like @Txhayseed said, check your pressures. I think there is a coupling between the motor and pump that can break too.

Boom lift function often didn't work on Aux. even when fairly new. Aux. was Usually just good for going down, tilting/swinging the basket and a bit of telescope. Should swing the boom too.

Thanks for the replies and suggestions, after tearing into this I discovered the electric motor (which looks to be nearly new) rotates CCW as opposed to CW which the pumps required. I moved the field windings 180 degrees to reverse direction and the auxiliary function is now working although does seem weak on boom raising and lowering. Seems like it should be adequate to get down in the event of a problem with the gas engine though

Raising the boom is the hardest thing you can ask 12 volt aux pump to do. Lifting 6k straight up. No matter the boom or it’s age I’ve never inspected or used a boom that wanted to lift the main boom with out some effort.
that’s just normal and remember it’s designed as a redundant emergency use system. Lowering is also going to go Slow to allow the recovery to
Be done in a controlled manner. Glad you got it figured out and your up
And running