My KX161-3SS has a thumb issue. When the thumb switch is activated, the thumb immediately goes to the up position and puts a load on the machine. The rocker switch will operate the thumb but as soon as you release the closing operation it opens back to the full range.
Having similar issue. Did you get any advise. In my case, a 2010 CAT 303C CR this occurs if you touch the thumb switch after starting the machine. If I stop a restart the excavator, the thumb stays where it is as long as I dont touch the switch.
I'd check for power going to the solenoid valve when the switch is in neutral. Leaving a volt meter hooked up when operating the switch could tell what's going on. It sounds like either the switch is bad or something is shorting out putting power to the solenoid when in neutral or after using the thumb. Another thought is the control valve is sticking or the centering spring is weak or broken. Was the thumb working properly and the issue came suddenly or it was always a problem?
Was working correctly before. If the valve would be the problem, it would not reset when we restart the engine. We tried disconnecting the vavlve and it stopped going back. Suspecting bad swith or bad switch contrôler in the joystick
Definitely sounds electrical if it stops when disconnected.