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Komatsu "Four" (safety) System

MrEvilPirate

Active Member
Joined
Sep 21, 2021
Messages
37
Location
CT
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.
 

Dutchboy

Member
Joined
Dec 27, 2016
Messages
16
Location
Upstate
I have a PC-50 also. The system can be very problematic to say the least. i ended up bypassing the control spool. Then it is operator skill to keep from hitting the cab. :) Your control spool is under the floor of the cab and has 9 hoses going to it IIRC . Splice the 4 on one side straight across to the 4 on the other side and plug the 9th which will be oil bypass. Got the fittings at discounthydraulics.com. Should be JIC 10? IIRC
 

MrEvilPirate

Active Member
Joined
Sep 21, 2021
Messages
37
Location
CT
Hey Dutchboy thanks for the reply. I will take a look under the floor and try to find the control spool. I have jumped the cancel switch and I can work the machine, but it is a little funny now... boom up keeps going for a second or two after I release the control sometimes. Not sure if that is linked. It also gets super slow now after about an hour, didn't do that before.
 

John C.

Senior Member
Joined
Jun 11, 2007
Messages
12,865
Location
Northwest
Occupation
Machinery & Equipment Appraiser
The system you describe was pretty common on gray market machines some years ago. I've seen plenty of them and there are differences between model years and machine models. PM me your email address and I'll send you what the info I have. The systems were an add on and I don't believe they are supported by Komatsu.
 

Dutchboy

Member
Joined
Dec 27, 2016
Messages
16
Location
Upstate
My machine is a ser. 9945 . According to my repair manual the main difference between mine and yours would be mine is a gear pump and yours could have a variable displacement ( hydro style ) pump. Your pilot system should be the same. I got mine reasonable because the prior owner was having the same symptoms. I repaired wires on the potentiometers and got it to work intermittently. Because of the cost/availability of the potentiometers and controller decided to bypass the system. The system doesn't keep you from catching your blade or track so i consider the value of it debatable at best. It is a 20+ year old computer :) Mine is a 1996 model. I have had mine bypassed for 5+ years and haven't missed it a bit.
 

MrEvilPirate

Active Member
Joined
Sep 21, 2021
Messages
37
Location
CT
For record for anyone who comes after me... the document I received from John C was a section of the service manual. Same info that was in mine, wire colors didn't match up, and my efforts to "reset" the system did not work.

My cancel switch has been jumped this week so I could use the machine. Boom up is VERY slow after about an hour of use. I found that if I was curling the bucket (keep curling with a log or something in there) then the boom would move at regular speed. So I don't think there is anything wrong with the hydraulics. More like a pilot control issue? I'm wondering if that computer is still messing with something even though it is canceled. I will open the floor this week and take a look at what Dutchboy suggested.

Dutch - did you remove the computer entirely as well or just bypass the control spool? I need to open it up and take a look then sit down with my manual and digest. I am new to hydraulics. Thanks.
 

Nige

Senior Member
Joined
Jun 22, 2011
Messages
28,979
Location
G..G..G..Granville.........!! Fetch your cloth.
Boom up is VERY slow after about an hour of use. I found that if I was curling the bucket (keep curling with a log or something in there) then the boom would move at regular speed.
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.
 

Dutchboy

Member
Joined
Dec 27, 2016
Messages
16
Location
Upstate
https://www.discounthydraulichose.com/thread-identification-tools-96769.html If you go to this site it will allow you to download a guide to figure out which fittings you have. You will need 4 of a fitting that looks like this part # Part #: 2403-06-06 and 1 of these Part #: 2408-10
2408-10 | 5/8" JIC Tube Plug
.This not for sure the right size or the right flare. Did not have time to match it up, may have time this afternoon. You should be able to match it up with that guide. Your symptoms are mostly the same as mine and your experience is frustratingly similar if that's any consolation!? You say it speeds up if you are using 2 functions, that i can't remember. My boom down (most times) and arm out were normal and boom up arm in would be at SUPER slow speed. After i confirmed everything worked correctly w/out the spool I did remove the spool and the computer behind the seat. If I was in your situation I would get the fittings ( they should be under $100) and bypass the valve to see if that fixes your problem BEFORE I remove the valve or try anything else. I am fairly confident this is your problem. If this doesn't fix your problem you can put it back the way it was and proceed farther with less expense than a basic service call. Let us know how it works and if it does solve the problem be sure and post the correct part #s and sizes.
 

Dutchboy

Member
Joined
Dec 27, 2016
Messages
16
Location
Upstate
I am going mostly off memory from 5 years ago. can't remember if there is 4 spools or 3 on the valve but you will be looking for a valve bank under your right foot when you are in the seat and it should have 9 maybe 7 hoses going to it with 3 or 4 electric solenoids on top of it. Got to run , let me know if you need more help.
 

MrEvilPirate

Active Member
Joined
Sep 21, 2021
Messages
37
Location
CT
DB thanks buddy. I'll head out to the woods this week and take a pic of what I see under the floor and match it up with my service manual. Appreciate all the help.
 

John C.

Senior Member
Joined
Jun 11, 2007
Messages
12,865
Location
Northwest
Occupation
Machinery & Equipment Appraiser
What Cat people call resolver valves are generally known in the industry as shuttle valves. Komatsu only used them in the pilot systems to allow pressures from either side of a pilot operation to operate a pressure switch at the same time. For instance boom up and boom down both used to operate the same pressure switch. I believe now each has its own pressure switch. Another use would be for a straight travel pedal installed in addition to two separate travel pedals.

The issue with this machine is that the pilots are controlled by a separate valve bank which is solenoid operated and those a controlled by a microprocessor. For what ever reason the microprocessor is not letting two pump function operate when it would normally be called for.
 

heymccall

Senior Member
Joined
Feb 19, 2007
Messages
5,349
Location
White Oak, Pa
The system can be made to sound very convoluted by reading the manual.
Having 2 Komatsus with this system, it really is straight forward.
I have a PC128UU-2 and a PC228UU-1.

Each potentiometer can be disassembled and inspected. Just be sure to remove the woodruff key before removing the guts. In my experience, the wiper fingers or wiper paths wears out.
It's been a little while since I played with them, but, if there is a bad spot in one of them, the system locks out, requiring the override.
And, when in override, only one pump runs the boom, at reduced pressure.
Once you disassemble one of them, you can figure how to measure its resistance thru its range, allowing you to measure the others without disassembly.
 

John C.

Senior Member
Joined
Jun 11, 2007
Messages
12,865
Location
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Occupation
Machinery & Equipment Appraiser
Caps and plugs are officially JIS but the hose and fitting people just call them Komatsu.
 

MrEvilPirate

Active Member
Joined
Sep 21, 2021
Messages
37
Location
CT
Hi everyone. Wanted to close the loop on this one. There are trouble codes listed in two different sections of the manual. I was using a procedure to reset the system which requires you to hit the override switch, offset full right, boom up, stick in, full curl. I was getting error 61, or 34 if I turned off the over ride. These were both not listed in the trouble codes for the resetting the system.
There was another section in the manual for troubleshooting the 4 system. That had my codes. 61 is for when you have moved the arm into the danger zone and the system should have stopped it. The override switch had allowed me to do this. I chased it for a while until I realized what was going on. Code 34 is tied to the offset boom. I removed the connector, cleaned it real good (some gel-paste goop in there) and re-crimped it. 34 code went away, machine was working fine.
As Dutchboy mentioned, the slow boom up must have been tied to the fact that I was using the override.
The machine is working great now except for a slow dozer blade (this is direct hydraulic, no computer between the lever and the spool).
The manual for this thing is not great. Thanks for the help.
 

Chris Voorhies

New Member
Joined
Jan 26, 2023
Messages
1
Location
Michigan
The system you describe was pretty common on gray market machines some years ago. I've seen plenty of them and there are differences between model years and machine models. PM me your email address and I'll send you what the info I have. The systems were an add on and I don't believe they are supported by Komatsu.

We are experiencing the same issue as MrEvilPirate did on June 21, 2022. Could you send us the same info that you sent him please?
 

gregmr

New Member
Joined
Sep 30, 2017
Messages
4
Location
Cawongla
https://www.discounthydraulichose.com/thread-identification-tools-96769.html If you go to this site it will allow you to download a guide to figure out which fittings you have. You will need 4 of a fitting that looks like this part # Part #: 2403-06-06 and 1 of these Part #: 2408-10
2408-10 | 5/8" JIC Tube Plug .This not for sure the right size or the right flare. Did not have time to match it up, may have time this afternoon. You should be able to match it up with that guide. Your symptoms are mostly the same as mine and your experience is frustratingly similar if that's any consolation!? You say it speeds up if you are using 2 functions, that i can't remember. My boom down (most times) and arm out were normal and boom up arm in would be at SUPER slow speed. After i confirmed everything worked correctly w/out the spool I did remove the spool and the computer behind the seat. If I was in your situation I would get the fittings ( they should be under $100) and bypass the valve to see if that fixes your problem BEFORE I remove the valve or try anything else. I am fairly confident this is your problem. If this doesn't fix your problem you can put it back the way it was and proceed farther with less expense than a basic service call. Let us know how it works and if it does solve the problem be sure and post the correct part #s and sizes.
Mate JIS fittings ,4 of 14mm JIS nipples to bridge hoses across 4 valve block under right foot ,plug remaining hose, cap old fittings by bridging with old water hose.BUT be very careful ,if the hand ,eye ,brain coordination a bit slow the bucket closeness to the cab and you ,will frighten you sometimes
 

topgut

Active Member
Joined
May 19, 2023
Messages
28
Location
NEPA
Make sure your alternator is putting out 13 volts. i put a new one on my PC28uu-2 and it fixed my slow to move problems that were like the 'Four system' . I put the story in my thread last week.
 

postmortem_42

Member
Joined
Oct 30, 2023
Messages
18
Location
Cleveland GA
Hey guys, new to this forum and just purchased a used PC28UU-2, S/N 10274. I am having similar issues to the above safety feature with the momentary override switch wired to always on. I have looked under my floorplate for a valve block under right foot but this appears to not be what is being described. However, under my left foot and to the rear is a valve block with 4 solenoids with 3 smaller/1 larger hydraulic lines going into to top and some small/large ones exiting side. If this is it, I can't really tell which lines to bridge and need some help in doing so. Any help would be greatly appreciated as the arm moves very slow, but all else is ok. Thanks
 

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