KOMATSU PC75 UU-2

[Mike59]

Hi Guys, Problem with the PC75 digger again. If we turn the ignition key one click from the ‘off’ position, all ignition lights/gauges come on & we get the ‘ticking’ sound from the ECU behind the seat. The ‘ticking’ then stops after about 10-15 seconds & we lose the fuel gauge & coolant temperature at the same time. If we repeat this from the off position, same thing happens each time, but we lose the functions almost immediately. When we turn the key to start, she fires up & runs with no problems at all.

She’s an old machine & the wiring loom is a bit of a mess, so obviously an electrical fault somewhere. We’ve got a big digging job to do in a few weeks, so need that fuel & temperature gauge working. Any thoughts/ideas of where to look ? or a possible workaround with some new wire ? Any help gratefully appreciated.

 

[V8Druid]

check out your bird's nest of a wiring job first to see if anything obvious shows up, but if the gauges are 'fed' by the ECU you have a job on your hands

 

[CPS]

Check your earth straps etc. Also check the battery isolator if it's an ignition type one.

Also something is telling me if komatsus have a bad alternator they do strange things like this Also. Check that it is charging when running

 

[Shovelhands]

Check your earth straps etc. Also check the battery isolator if it's an ignition type one.

Also something is telling me if komatsus have a bad alternator they do strange things like this Also. Check that it is charging when running

Alternator was my first thought, with it being a Komatsu!

First check is unplug the alternator and see if the symptoms remain.
I had one that randomly fecked around, was the alternator, but it was charging and never had a flat battery etc. weird stuff indeed….

 

[CPS]

Alternator was my first thought, with it being a Komatsu!

First check is unplug the alternator and see if the symptoms remain.
I had one that randomly fecked around, was the alternator, but it was charging and never had a flat battery etc. weird stuff indeed….

Yea, seem to recall a head scratcher with a Komatsu once

 

[Mike59]

Many thanks for your replies chaps. I’ll try disconnecting the alternator & see what happens then. Will report back with the result. Cheers Mike

 

[Mike59]

So have spent hours on it today. Checked battery relay/ignition isolator & cleaned all connections - no change. Disconnected plug from alternator - no change, so reconnected. Checked visible parts of wiring loom - no obvious damage or breaks that I could see. Could be a diode or some other fault in the alternator I guess, but wondering if it could be the ECU itself & not sure it’s worth getting into that. I think I’m going to live with the problem for the time being. Tracking & hydraulics are all working, so I’ll just have to make sure fuel & coolant levels are fully topped up, if the gauges aren’t working. It’s a 25 year old machine, so bound to have some faults.

 

[Canal Navvy]

You'd almost think that the gauges were taking their live feed from a glowplug timer/relay

 

[Mike59]

You'd almost think that the gauges were taking their live feed from a glowplug timer/relay

Yes, I see what you’re thinking. I’ve got a copy of her wiring diagram, which I had blown up supersize to make reading easier. Trouble is you can spend hours reading those things & it still doesn’t tell you where the problem is.

 

[Mick-the-fitter]

Take the wire off the fuel sender and temp sender! Does it still do the same?

 

[Mike59]

Okay I’ll try & locate them both/try that & report back. Everything is packed in so tight on these zero swing machines, it’s hard to get at stuff !

 

[Canal Navvy]

When the gauges are working do they read believable values ?

 

[Mike59]

When the gauges are working do they read believable values ?

Yes, the fuel gauge does, albeit for just a few seconds & the temperature gauge has always been accurate - need to look at it again when the machine has been working for a while.