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I have a Cat 312B that will crank but shut off in 5 to 10…

I have a Cat...

I have a Cat 312B that will crank but shut off in 5 to 10 seconds and blow the 15 amp key swithch fuse. It will also blow the fuse even if you dont crank the engine but just turn the switch to the on position

Mechanic's Assistant: What is the complete model and serial number of your machine?

2000 Caterpillar 312B excavator SN 9hb 27240

Mechanic's Assistant: Sometimes things that you think will be really complicated end up being easy to fix. The Construction Equipment Mechanic I'm going to connect you with knows all the tricks and shortcuts.

Ok

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Customer reply replied 3 years ago
Posted by JustAnswer at customer's request) Hello. I would like to request the following Expert Service(s) from you: Live Phone Call.Let me know if you need more information, or send me the service offer(s) so we can proceed.
Answered in 4 hours by:
6/1/2019
Mechanic: catmastertech, Technician replied 3 years ago
catmastertech
catmastertech, Technician
Category: Construction and Road Equipment
Satisfied Customers: 3,969
Experience: Field service technician for CAT 19 years.
Verified

Hey, sorry to hear you are having these problems. I know that can be frustrating. Hopefully, we can get you back to work quickly. I see no one could help you earlier, I hope this is not too late to be helpful. Please note that I am not set up for phone calls, please ignore the site pop-ups. We can post to this chat and work through this issue. All experts are not employees, we work from home in our spare time to answer questions.

Can you post the machine serial number? The one you posted earlier is the engine serial number.

Please note, if this is a grey market machine I will not likely have the correct information to help. It may be close but, it is never completely correct.

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Customer reply replied 3 years ago
its a 2000 312B made for Japan. I have S/N 9HR012742I pulled out the key switch to see if there were any corroded wires but found none. It looks like on the schematics that i have that the ignition fuse is combined with the refueling relay? I just can figure out where that would be. I understand that it may not be the same schematic.
Mechanic: catmastertech, Technician replied 3 years ago

Do you have a number related to the fuse or can you send me an image of the fuse that fails so I can be sure I am looking at the same one you are?

BTW I see 8JR machines here often and it matches to a 9HR as well... maybe it is closer than I thought.

I do not see the refueling relay as part of the key switch circuit. This is a very rare option, does your machine have this refueling pump option?

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Customer reply replied 3 years ago
it does not have it but the refueling fuse is the next one down and the backside of the panel is has a jumper between those 2?both are 15 amp fuses in the middle of the panel
Mechanic: catmastertech, Technician replied 3 years ago

You are looking at the supply side of the power from the 177 battery feed to the fuses. The key switch fuse is only on the 105 red wire.

The problem is you said the fuse only blows when the key switch is on. That means the short of after the key switch on the Yellow 308 wire.

That means all the functions that are powered by the key switch are suspect.

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Customer reply replied 3 years ago
ok is there anyway to isolate that
Mechanic: catmastertech, Technician replied 3 years ago

A common fault I have seen if the Air Inlet Heater Control Unit. Try unplugging this control to see if the fuse will stop blowing.

See item(###) ###-####in the relay panel.

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Customer reply replied 3 years ago
the relay panel behind the cab in the main power box?
Mechanic: catmastertech, Technician replied 3 years ago

Then try disconnecting the Fan Relay(###) ###-#### It should be in the upper right corner above the timer relay.

After that, the main relay (large one in the center) could be the issue. I had to replace three of them last year as they just suddenly decided to fail to completely different machines.

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Customer reply replied 3 years ago
ok, Im not at the machine right now. I will try those things and get back to you. Thanks for your help
Mechanic: catmastertech, Technician replied 3 years ago

Ok, look for the ones that are controlled by the 308 YELLOW wire. I believe that is where your short will be.

If the Heater Control unit or the Fan relay don't change the problem, try a new main relay and that could solve this issue.

Odd thing was they all failed last year right about this same time.

Good luck, Don

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Customer reply replied 3 years ago
ok will do. thanks
Mechanic: catmastertech, Technician replied 3 years ago

Thank you for using JustAnswer, if you do need further help please let me know.

If you are satisfied with my service, please take a moment to provide a rating.

Thanks again, Don

CATMASTERTECH

catmastertech
catmastertech, Technician
Category: Construction and Road Equipment
Satisfied Customers: 3,969
Experience: Field service technician for CAT 19 years.
Verified
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