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Curtis B.
Curtis B., Technician
Category: Construction and Road Equipment
Satisfied Customers: 1231
Experience:  Technican turned service manager with multiple lines of equipment and rental units.
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I have a 330 C CAT excavator Serial prefix CAP, my issue is

Customer Question

I have a 330 C CAT excavator Serial prefix CAP, my issue is the machine was functioning correctly one second I locked the hydraulics out jumped out, jumped back in threw the lever and was going back to digging and I lost all hydraulics, I switched the horn and lock relays and had no difference, I can hear the relays functioning, I hooked up ET and I have pump pressure as I am supposed to. I can not seem to locate the pilot valve solenoid or even if that is where I should check, I have a single green light lit on the hydraulic control ecm. I need help I am in dire need of this machine
Submitted: 2 years ago.
Category: Construction and Road Equipment
Expert:  catmastertech replied 2 years ago.
Hello, Please post the full machine serial number so, I can answer your questions correctly.I assume you what to find the hydraulic lockout solenoid?Can you see the lockout switch function on ET? Does it change status when you move the lever?Have you tried the backup mode?
Expert:  catmastertech replied 2 years ago.
The lockout solenoid is part of the pilot manifold group and is located under the main control valve with the other control solenoids.
Customer: replied 2 years ago.

Would that prohibit movement of all hydraulics, how do I test pressure from the main pump it seems quite load all of a sudden. Do the pumps just fail all of a sudden. I think I tried the back up mode but I only have motor functions. I know the lock out handle is function as the machine will not start with it engaged, I did not see it in ET but I am not that fluent with it yet the whole serial number is *****

Expert:  catmastertech replied 2 years ago.
The backup will override any issue that is controlled by the ECM controller. It will not bypass a harness problem or switches not in the controller systems. The neutral switch has two parts, one is for starting, (neutral start) and the other is for the hydraulic lockout function. I think ET will show the status of the switch on separate screens, this may be different depending on the version of ET you have. ( I am not certain, I just remember seeing it on some machines)
Expert:  catmastertech replied 2 years ago.
The neutral switch receives power from the timer relay on the RED wire (machine harness, not switch harness) marked 189.When the lever is down for neutral, the switch send power to the neutral start relay on the RED 154 wire.When the lever is raised, the power is sent to the hydraulic lock relay on the GREEN 151 wire.
Expert:  catmastertech replied 2 years ago.
From the relay power goes out to the solenoid on the A588 GREEN wire. A quick test of the circuit would be to check resistance at the A588 green wire in the relay at its Normally Open terminal and to ground. If the circuit is good, this will read the resistance of the coil in the solenoid and your reading should be about 32 ohms. If the reading is very high, test the solenoid directly at the connection. If it is very low, (less than 5 ohms) the wire is shorted to ground. Below is an image of the relay connections.
Expert:  catmastertech replied 2 years ago.
Let me know what you find and if I can help you further. Thanks, Donnie
Expert:  catmastertech replied 2 years ago.
I missed the first part of your question.No, the pump do not fail suddenly. It more likely to hear loud noises and feel it weak and vibrating before a major failure.However, this pump does have a drive coupling that can fail and you will lose all functions. If you remove the accessory drive cover next to the pump and it is not turning when you crank the engine, the drive coupling has failed.NOTE; oil will leak out the housing when you remove the cover. If this is only a pilot control issue, you should still have standby pressure and pilot pressure at the pump. You only need the hose connectors to test the pump pressure for PRV and pilot pressure. Pump output pressure can be viewed in ET. (PRV pressure shown in ET and the monitor is a calculation, a test gauge must be used to set the correct pressures)(PRV is sometimes called powershift pressure)
Customer: replied 2 years ago.

I did see pump pressure on et at an idle it was around 800 psi. I will try to test the above as specified and advise thanks for the help

Customer: replied 2 years ago.

And you said the lock solenoid is under the main control valve accessed from the below the house?

Expert:  catmastertech replied 2 years ago.
Yes, look for access plate close to swing bearing just forward of the engine access cover.​
Customer: replied 2 years ago.


Tested the circuit I get like 35 ohms from the A588 wire to ground.

Pulled the access cover cranked the engine and the gear turns...the gear is pretty chewed up I might add.

I pulled the solenoids as I was already there they look fine but did not want to energize as I do not know what voltage the are I would think 24 volts but ws not certain since the label was painted over. I am kind of stumped as to whereto head next as I was fairly certain it was going to be the lock out solenoid.

Pleas help my back up machine is an prehistoric JD 792...

Thanks in advance

Expert:  catmastertech replied 2 years ago.
The lockout solenoid is good, no problem there. You should have almost 600 psi pilot pressure if you test at the tap next to the small pilot oil filter. If not I would change the pilot filter and cut open the old filter. If you find metal in the filter, your pump drive gear bearings have failed and sent metal through the pilot pump causing the loss of pressure. The pilot pump is inside the housing and the pump assembly must be removed to access it. When you remove the pilot pump you can see the drive gears and bearings better to confirm the failure.If you have pilot pressure, you will need to check the solenoids again. All three are the same so you can swap the single one with either one of the pair of solenoids. If this does not help, look for a blockage to the pilot block under the cab were all the pilot controls receive their pressure.
Customer: replied 2 years ago.

I tested at the tap and get zero pressure, I know its not my gauge as I tested the main pump and get around 500 psi at an idle, is the pilot pump load sensing? I just hate having to tear it apart not knowing for sure...however no pressure is a great indicator.

Expert:  catmastertech replied 2 years ago.
Did you check the pilot filter?
Expert:  catmastertech replied 2 years ago.
The pilot pump is a simple gear pump. If it is good, it will pump oil.The only issues that effect it are failure of the drive gear or failure of the pump. You can check the relief ​valve to see if it has any debris stuck in it. The pilot relief is in the same housing as the filter and the pressure tap is next to it.