Was using my excavator this week with no issues until today. First start in the morning was fine, though I notice the battery light was on at idle and faded out when I brought the engine speed up to working. Later in the day, it would not start at all. But even stranger was that when I turned off the ignition and removed the key, these three lights remained on. The grid heater will not work either, though I hear some solenoid click when I turn the key to that position. When I turn the key to START position, I hear no click whatsoever. I tried disconnecting the battery positive terminal and reconnecting it again and the lights went off and stayed off. However, on the next attempt to start the machine, the lights are stuck on again. It's exactly as if ignition were in the on/acc position. Fan and lights will turn on when switched. Battery voltage reads 25.5 V and each battery reads about 12.5 V. Is this behavior typical for batteries that can't deliver enough current to engage the solenoid? These batteries are of unknown age, from Wal-Mart, put in by previous owner. I've got a charger on them now, and will see if it makes any difference.
You probably need to give a full model and serial number. (I hate having to say that, it is the first reply on about 80% of threads.) Once these guys know what pc60 you have you will get a lot more and better information. To tide you over until the smarter guys show up I have an idea or two. On most komatsus that I deal with, there is a battery relay near the battery. Kind of looks like the ringer on the phone from "little house on the prairie". Should have two heavier gauge wires for power delivery and two smaller wires for signal and ground. That is the first place I would look because it sounds like yours has the contacts fused closed. I am not sure how to explain this. When you turn the key to on, the signal wire to the relay activates the relay to close the circuit and then power is applied to the rest of your key on circuits. When you turn the key to off, the power to the signal wire on the relay is interrupted and opens the contacts in the relay. This is where I am not sure how to explain the rest. (And to be perfectly honest; I would like someone else to explain it to me). On most of the machines I work on it takes a couple of seconds between the key going to off before the battery relay returns to its normally open state. I could just keep typing about why I think that is, but... With your symptoms I think that battery relay is most likely. Next best suspect is your alternator. I can honestly picture you reading that with disbelief. Hear me out. These machines are designed so simply that logic takes a back seat. Your ecu has no idea how to determine that the engine is actually running. Komatsu uses the signal from the alternator to tell the ecu that the engine is or isn't running. So, when your alternator is shorted out (in a way that doesn't actually affect charging) the ecu sees that the engine is still running and then doesn't cut power to the battery relay.
Thanks for that ECU information. More info, the model is PC60-7. Don't have the s/n with me now. Will have to go out in the daylight to find that. New discoveries: The alternator belt is real loose. I mean REAL loose. As in over 3/4" of play when you press on it. I was going to adjust the alternator bolts to tighten it, but frustratingly, the $400 in Harbor Freight wrenches I bought 2 years ago skip over the 18mm box wrench size. I have 15-17mm and the next size up is 19-22mm! Why there isn't an 18-20mm in that kit, I do not know, but now I have to go out and buy an 18mm wrench. The solenoid/relay in series with the battery releases when I disconnect the battery. So your hunch about the ECU may be correct. But I hope the alternator is not shorted. It's not in a place I can access, being at the back of the engine bay against the firewall. I cannot even SEE the lower pivot bolt for it. So, it's off to Harbor Freight again tomorrow for a wrench, then I will try to tighten the belt. I have a charger on the system now and will let it charge overnight.
After charging the batteries all night, the engine still won't start. The panel idiot lights only dim 10% or less when the key is turned to START position. I have voltage at the starter solenoid. Interestingly, the first time I turned the ignition and then off, all the lights turned off normally. The second time, I tried the heater position and the green light came on. So next I tried to start the engine, but nothing, not even a click. Just a slight dimming of the lights. At this point, when I turned the key off, the lights remained on. And the heater position no longer lights the green light. In the interest of being able to use the machine, is it safe to turn ignition to on position and then jumper the small terminal on the start solenoid to the battery terminal to engage the solenoid? My concern here is damaging the electronics by backfeeding voltage here. Or, I could disconnect the small wire to the starter and jumper the terminal to the battery side of the solenoid to prevent backflow to the rest of the electrical system. I did the following test on the batteries. I put a 5 ohm 100 watt resistor across the hot and ground and measured each battery voltage. I had 12.95 and 12.87 volts respectively, so I don't think the batteries are bad. This was after charging all night at a constant 10A rate. I do think it odd that the charge rate did not drop overnight though. It was 10A when I started charging last night. What do you folks think about the condition of my batteries? BTW, I did manage to loosen the alternator bolt and tighten the belt.
Interesting Update: I turned the ignition switch on and hot jumpered the start solenoid. Engine started. Ran normally. As I mentioned, I was able to tighten the tension on alternator belt. I ran it a few minutes and then shut it down. It shut off normally. No lights stuck. I started it again and it started right up. I did notice that on low idle, the battery light glows. It fades out if I raise the fuel lever to half speed setting. My hunch is that the last time around, it didn't shut down correctly and left the ECU in some odd state. It needed a running engine to properly get all it's signals back in the right sequence. I suspect it's time for new batteries though. Maybe that battery light is indicating improper charging of the batteries due to their age and having sat for several years with very little use. So I think I'll buy a pair of deep cycle batteries and see if that solves the remaining issue.
Installed two new Die Hard deep cycle batteries (1000 CCA) today. Cleaned up the battery bay while I had it apart. Machine starts and runs fine and shuts off normally now.
I am a little surprised that no one else jumped in on this thread. Komatsus seem to be a little unpopular on this message board. But, I have gotten some pretty vital info from JohnC and lachau in the past. I thought they would weigh in. I am crossing my fingers that you have this solved. Kind of makes sense. Underperforming alternator (loose belt) and worn out batteries (pulling amperage after 8 hours on a charger) probably would cause this issue. Still, was hoping for someone to explain the delay between key off and battery relay off.
Me too. Why a weak battery would cause the battery relay not to release. I can only think it's a positive feedback loop design error in the ECU programming. "The battery is weak, so why don't we kill it altogether by forcing the ignition on."
Your batteries might have been OK but why did you put deep cycle batteries in? They aren't really designed for starting demands where you want max. amps in a short amount of time.
This is what I bought. 1000 cranking amps ought to be plenty. Better than the wal-mart batteries the other guy had in there. Bigger too. I chose this type because they have a deeper well for sulphation deposits.
OK, that's not a true deep cycle battery but a combination starting and partial deep cycle. Should be more than enough to spin the engine over.
I think it should be the ideal battery type for intermittent use like this. Machine has been starting and running and shutting off normally since the battery install.