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Komatsu PC120 no start

Ron/RPMS ยท 2021-09-09 20:38

A little intro; I am a former auto mechanic(ase) , former automotive machinist (ase), now industrial machinist. I drag race and build hot rods and drag cars as a side job. Now with that said I am trying to help one of my racing buddies fix his Komatsu PC120 excavator and I am not familiar at all with the machinery. There is no voltage at the key. Is the voltage supposed to be 12V or 24V at the key switch? The battery relay is not pulling in . The engine will start if we jump the two large cables on the battery relay and then jump the solenoid at the starter. Batteries are new. Fuses in the fuse panel are good. Circuit breakers have continuity . I did a search and read about diodes but I am not sure if that is the route I need to go. Can someone point me in the right direction of troubleshooting? Thanks. Ron................

Replies6
  1. #1skata2021-09-09 21:48

    Is there a battery disconnect somewhere by chance?

  2. #2John C.2021-09-10 10:29

    The machine electrical system is all 24 volts. You will need to provide the full model designation. It can be a Dash 3, Dash 5 or Dash 6 or higher. Here is a short video describing the battery disconnect switch. Remember to check voltage at the battery cable ends as well as on the battery terminals themselves.

  3. #3Ron/RPMS2021-09-13 19:25

    Thanks for responding. Owner has owned it for 15 plus years and as far as he and know there is no disconnect switch .

  4. #4Ron/RPMS2021-09-13 19:26

    Thanks for responding . I will view the video and contact the owner and get the rest of the information.

  5. #5Ron/RPMS2021-09-17 06:19

    The machine is a 1997 Komatsu PC120-6 Advance. He changed the battery relay and still no start. I will be going out there tomorrow to do some more troubleshooting. Thanks

  6. #6John C.2021-09-17 12:25

    There are fusible links installed above the battery disconnect that look like wires. I forget the amperage but they have been known to fail. The battery cables are another source of trouble as are the ground connections to the frame and I believe the battery positive cable goes directly to the starter. One fuse on the fuse box in the cab is supposed to be hot all the time and you need to actually test both sides of the fuses with a multi meter or a test light. The center connector wire can appear to be intact and the fuse still be bad.