What could cause forward and reverse drive failure on a JLG E300AJ if the shunt wiring checks out but a 7740 code still shows?

[Nicholas Villa]

I'm still learning my way around electrical troubleshooting and could really use some help on my JLG E300AJ.

Everything else works fine, but I've completely lost forward and reverse drive. I'm getting a 7740 code that points to the shunt circuit. I already checked the wiring and continuity, and everything seems okay, which is what's confusing me.

What I don't really understand is how the shunt actually works, since all 3 wires are connected to the same bar. I'm not sure what exactly I should be testing or looking for.

 

[BorjMaybury]

Had a similar issue on an older Genie lift once - wiring checked out fine, but it ended up being a bad connection at the controller plug causing the drive functions to act dead.

 

[Harvey Esteban]

If the wiring and continuity check out, I'd probably start looking closely at the controller connections and the shunt itself. I've seen electrical issues where everything looked good on paper, but a corroded pin or weak connector was enough to trigger a fault code and disable drive functions. Sometimes the problem is hiding right where you least expect it.