Komatsu "Four" (safety) System

MrEvilPirate · 2022-05-25T00:02:29.000Z

PC50uu-2 serial 14484. This machine has an offset boom. This "Four" system prevents you from taking a bite out of the cab when the boom is offset in the left hand position. It also lets you set max height and depth for the boom/stick. There are potentiometers for the boom, stick, and the offset. They talk to a controller in the cab. There is a console that can give you info like what depth you are digging at... that display is supposed to show error codes when there is a problem. There is also a dummy light that flashes when there is an issue with the system. When there is a problem with the system it locks you out from raising the boom, pulling in the stick, or off setting to the left. There is a "cancel switch" under the seat that over rides this so you can get it into a safe spot or get the machine into the correct position to do a reset. My manual has a procedure for reset you boom up, stick in, bucket curl, and full off set right. Then there are some wires you are supposed to connect and you get an error code or successfully reset. The wires I have don't match the description (colors) in the manual, something happens when I connect them because the dummy light flashes in different pattern but I don't get error codes displayed and the "reset" is not successful. Has anyone dealt with this? The existing cancel switch is momentary, you have to hold it up then it pops back down to the default position. I am considering just replacing it with a 2 position switch and just cancel out the system. I called Komatsu dealer they won't touch it since it is grey market. They recommended a local independent guy. I talked to him for about 20 minutes, he said every time he needs to deal with these systems it is always a box of worms. He is also busy for the next several weeks. Any ideas guys? All connectors to the pots look good. Machine was running fine yesterday, I was lifting some brush off a trailer, dragged the bucket off the trailer it bounced a bit that's when the light came on. It reset by itself the first time (power cycling the machine) but the limiting function would kick in really early (bucket several feet from the front blade). Now the light is on all the time.

Started by MrEvilPirateMay 25, 202248 replies

johnnygNew MemberJan 3, 2024#41
Hi postmortem_42 I final got to try wiring all 4 solenoid to the bypass switch , oddly it blow a 20 amp fuse behind arm rest right arm , but the by pass switch still has power afterwards oddly . There only one potentiometer on the boom connected.The very first pipe to aluminium block is disconnected oddly I don't see a joiner. You mentioned PCP could be burn out can you advise some more please of your experience of this is this pilot control pressure for short
postmortem_42Junior MemberJan 3, 2024#42
only three go the the bypass, the fourth (closest to back) should be wired to key on and not to bypass switch. This solenoid is associated with the PCP feed and should be key on wired. All others control boom, arm and offset and have both and in and out of the block.
johnnygNew MemberJan 3, 2024#43
Thanks a mill , I will try that
postmortem_42Junior MemberJan 3, 2024#44
just make sure you maintain a feed to and return from the junction block.
SpadmanNew MemberAug 12, 2025#45
I’m trying to replace the potentiometer on the arm of my PC50uu2. The position of the lever as found on my machine doesn’t seem to be correct. Can someone who has this machine look at this picture and compare it to your machine? I found a drawing in the service manual that has the pivot arm oriented to the right side rather than the left. Thanks.
oldtomJunior MemberSep 20, 2025#46
Nige said: John C will have more detailed knowledge on the system on your particular machine but a function running slow then running at normal speed when operated in conjunction with a 2nd function is usually the result of a problem in a resolver (shuttle) valve somewhere in the main control valve. The function of the resolver valves is to prioritize hydraulic supply to functions. Click to expand... Hey Nige you've been around 428 tooo long
Joseph KrohneNew MemberSep 2, 2026#47
Mike_27 said: yup, they are just unplugged. Click to expand... it cannot work if they are unhooked because the solenoids are normally on so they need to be powered for the machine to work unless someone altered the internals of the valves .
Mike_27Junior MemberSep 2, 2026#48
Joseph Krohne said: it cannot work if they are unhooked because the solenoids are normally on so they need to be powered for the machine to work unless someone altered the internals of the valves . Click to expand... someone jacked with the valves.
gregmrNew MemberSep 3, 2026#49
Mike_27 said: someone jacked with the valves. Click to expand... Connect pipes with JIS Niples

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