Genie GS-4390 Hydraulics or Electronics Issue

[SSam]

Hi, I have a Genie 4390 rough terrain scissor lift that has become unusable. It is the gas/propane version with the Ford 425 fuel injected engine. It is 2004, SN: GS9004-41818 so an earlier model.

The machine has two hydraulic pumps and manifolds, one for drive and one for all other functions. Dive seems to work fine. The other functions are only working intermittently. Sometimes the engine stalls when trying to use the hydraulics. Sometimes it appears the hydraulic pump is not doing anything and the electric aux backup pump kicks on and very slowly provides hydraulic power to raise or lower the lift. I am first trying to determine if my issue is wiring, ECU, hydraulic valves or the pump.

Question 1: how does the control system determine when the auxiliary backup electric pump should be used? Is it based on a pressure sensor? I could not figure this out from the schematics in the service manual.

I have looked over the manual and tried to pull error codes. I am getting the code "1, 2, 3" which does not correspond to a code in the manual.

I can't decide if I should focus the diagnosis on the hydraulic pump (pressure test) or be looking at wiring, sensors and ECU's. I had a squirrel issue earlier this year where they ate the coolant hoses, so it is certainly possible they destroyed some wiring as well.

Thanks so much!

 

[Joe1167]

I have the same thing going on with mine. Any luck?

 

[Joe1167]

I have code 07 when I try to go up and code E2 when going down with the platform.
It also steers very slow.

 

[SSam]

My issue ended up being a loose wire to the alternator. It was only by trying everything and some luck that I figured it out. I never was able to find out how the system determines when the backup hydraulic pump is used, I assume the intermittent alternator connection did some strange things to the control system. After fixing the connections it worked perfectly.