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Curtis B.
Curtis B., Technician
Category: Agriculture and Farm Equipment
Satisfied Customers: 28086
Experience:  Technican turned service manager on multiple lines of equipment and rental equipment.
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McCormick MC 100. PTO will not come on with implement

Customer Question

McCormick MC 100. PTO will not come on with implement attached, will come on with no implement attached. PTO solinoid reads 10.7 ohms. Voltage at the solinoid wires are about 5.9 volts (with no-implement-PTO turning). No PTO controller error codes. All service manual PTO controller checks made with only one failure--that is seat switch power wire does read to ground when key is off, as does the entire switched power circuit.
Submitted: 1 year ago.
Category: Agriculture and Farm Equipment
Expert:  Curtis B. replied 1 year ago.

I don't have manual, but in my little pea brain, the pto solenoid has to have battery voltage to work correctly./??? Is there a relay between the switch and the solenoid?

Customer: replied 1 year ago.
Hello, The solenoid is 12 V no doubt, though not marked. Power comes through "switched power supply", fuse #35, wiring, connectors, wiring, then a "PTO controller" (computer or PLC), then wiring and one connector to the solenoid. I do not know what the PTO controller does internally. All wires and connectors check out with less than 1 Ohm using a Fluke 85. The solenoid does read the right Ohms at 10.7. I do have a "service manual" though no service bulletin updates. I notice that the parts have been updated to "coil attached to valve plunger" --- at $461. A little high to just change parts as a diagnosis. As you might know, this McCormick tractor is just like Case/IH Maxxum before the New Holland buyout of Case/IH. I am by now pretty expert on the service manual-the answer is not there. Unless you have specific experience on this problem, you should try to switch me out to some one who does.
Customer: replied 1 year ago.
Looks like I have to give you a rating to send this message. There should be a rating of "incomplete" or something. I'll give an OK rating --but it should be really "too early to tell".
Expert:  Curtis B. replied 1 year ago.

Do you have battery voltage to the fuse? With only 5.9 volts to the solenoid valve, it is not going to work with any pressure on it . I can opt out if you like, but I see question has gone unanswered for a while! You have to get 12 volts to the solenoid, and for test you could run battery voltage direct to the solenoid to see if it will engage.

Customer: replied 1 year ago.
Hello, Yes, I don't know how the solenoid can fail to get voltage pulldown, but your suggestion is a valid test. If the direct wire up does not work, then the solenoid is bad--replace. If the direct wire up does work, then wiring, connector, or PTO controller is bad (somehow).
Customer: replied 1 year ago.
I didn't answer you question--- yes, fuse voltage is 13+ V at the same time 5.9 V at the solenoid.
Expert:  Curtis B. replied 1 year ago.

Seems like there is voltage loss before the solenoid. Relay?

Customer: replied 1 year ago.
No relay. Though I have no information about the contents of the "PTO controller" , I believe it to have a solid state switch doing the function of a conventional relay. Also, if I disconnect the solenoid wire from the solenoid, the PTO Controller errors out and won't send any voltage at all. Error=open circuit to solenoid. The connectors look clean. Any comments from previous experience on sources of voltage pull=down.
Expert:  Curtis B. replied 1 year ago.

You say solenoid ohms properly, so it does not seem solenoid coil pulling too much voltage.

Expert:  Curtis B. replied 1 year ago.

How does solenoid ground?Through second wire back to controller?Or to tractor frame?

Customer: replied 1 year ago.
Solenoid grounds through a second wire back to the PTO Controller. I have now run the direct wires to the solinoid tests. The results are: (1) The direct will start the PTO without load, (2) with direct wires, still no magnet effect to screwdriver, and (3) PTO will not start with a PTO shaft attached. Therefore, my conclusion is that solenoid is bad and circuit is good. My intent is to order solenoid. Please make one last reply and confirm whether you think this is logical.
Comment: Even though you were not the specific expert I had in mind, a fellow with some experience and some sense can always add --- and often that addition is enough to make the difference. Thanks.
Expert:  Curtis B. replied 1 year ago.

I agree , but before I ordered the new one, I would take out the solenoid valve and see if there is anything obvious that would cause problem.