I am having trouble with my Komatsu pc28uu-2 excavator , the boom and stick will not go up code 34 showing on computer . I have done some research on this issue as it seems to be a common failure of the safety system , I believe the potentiometers are bad but cannot find any information on testing them or what their output should be nor can I find any wiring diagrams of this system , to my understanding of what I have checked on them so far is that they are 5Volt reference and should put out a certain voltage in either direction and I am getting zip from the boom sensor which then cuts voltage to the spool valves and stops the boom , stick and left side swing to prevent damage to the cab . I can not find any of these sensors for sale anywhere . Does anyone have access to them anywhere or am I going to have to bypass this system ? I have seen other posts about bypassing this system and was wondering why no one has just wired the solenoids to a 12 volt keyed on ignition switch circuit to bypass instead of trying to bypass the hydraulic circuits without the safety bypass valves ? I have observed others saying that the safety bypass switch to move the machine only allows the machine to move the arm very slowly and this is because the computer is still in control of the voltage and only puts out enough volts to partially open the spool valves to move the boom and stick for service , they are not getting 12 volts , if you bypass the computer and give the valves their full 12 volts that they need the machine works fine . Not an expert on these machines by any means and just looking for input as to whether my assumptions are correct or not , I do not want to hurt the machine but see no other alternatives . Your input will be greatly appreciated . Thank you Joe Krohne
That uu in the model number usually designates a gray market machine so info is going to be mostly non existent in North America. I'm guessing here but from your description you have and angling boom and the depth control and safety system on the machine. Could you confirm that?
That is correct .
I have bypassed the safety system but did find inline diodes going to the spool valves that need to be there . Wired in a 12 volt keyed on hot wire to the spool valves and the machine works as it should but you must be careful not to hit your cab if working the boom offset . I wished to repair it correctly but cannot obtain the parts needed so it is what it is with this old machine .
The diodes should be looping across the feeds to the solenoids. I haven’t worked on a machine this small so don’t know where they mounted the computer that runs that system. The larger and older machine’s boxes had diodes that could tell you which component was bad. Do you know if yours has that?
Code 34 is listed as an abnormality in the offset-boom potentiometer circuit, so I would not condemn the boom potentiometer yet. Inspect and test the offset sensor, connector and wiring first. Confirm reference voltage and sensor ground at the connector, then back-probe the signal while moving the offset through its range. The signal must sweep smoothly without dropping to zero or reference voltage. Also inspect the sensor linkage and connector terminals; another Four-System owner cleared Code 34 by cleaning and re-crimping the offset-pot connector. I would not wire the solenoids directly to keyed 12 volts because that permanently defeats the cab-interference system. Please post the machine serial number because the wiring and parts vary between PC28UU-2 versions.