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The PTO will not engage, the rear hydraulics will not work either, (front loader works properly) and the forward reverse will not work either. I get the transmission warning light (yellow looks light a gear) and the stop light, and the hazard lights flash, also the exclamation point light comes on. I have checked tranny fluid and it is fine. Cant find any fuses blown either. Any one got any ideas????
 

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Is there a separate reservoir fo the hydraulic fluid? Mine does that when its low.

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I assume this all happened at the same time? Do you have powerquad or ivt? I assume hitch is not working but how about rear scv's? Sounds like you have electrical issue but hard to say exactly what for sure. Is the tachometer working? I have seen engine speed sensor cause some of these problems but should not cause hitch and rear scv not to work. Is rear scv electronic or manual?
 

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I assume this all happened at the same time? Do you have powerquad or ivt? I assume hitch is not working but how about rear scv's? Sounds like you have electrical issue but hard to say exactly what for sure. Is the tachometer working? I have seen engine speed sensor cause some of these problems but should not cause hitch and rear scv not to work. Is rear scv electronic or manual?

Tach sweeps back and forth and does not work correctly. MPH is crazy high, and yes all of this happened at the same time as far as I know. I wasn't using the PTO when the forward reverse stopped working. I found this problem later. Im not sure what a powerquad or ivt is? Where do I find this info? Also thank you guys...
 

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Power quad has a lever for gears 1-4 in straight line and you can shift on the go without clutching. There will be another lever for ranges A-D in an H pattern, you can shift on the go, but must use the clutch. You could have E & F ranges too. It can be coupled with a power reverser too, lever for forward/reverse, that can be shifted without the clutch on the go.


IVT is a variable speed transmission.


When were the two hydraulic filters changed?. Light could mean they are clogged. The differential case also has sump screen.


Crazy MPH sounds like ground speed sensor. It's same P/N as PTO speed sensor. You could swap them and see if that fixes MPH.


Also a low battery voltage cause weird things electrical to happen. When mine was low, one warning light/turn signal would flash on the dash and ROPS but turn signal switch & warning light switch was off.
 

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Power quad has a lever for gears 1-4 in straight line and you can shift on the go without clutching. There will be another lever for ranges A-D in an H pattern, you can shift on the go, but must use the clutch. You could have E & F ranges too. It can be coupled with a power reverser too, lever for forward/reverse, that can be shifted without the clutch on the go.


IVT is a variable speed transmission.


When were the two hydraulic filters changed?. Light could mean they are clogged. The differential case also has sump screen.


Crazy MPH sounds like ground speed sensor. It's same P/N as PTO speed sensor. You could swap them and see if that fixes MPH.


Also a low battery voltage cause weird things electrical to happen. When mine was low, one warning light/turn signal would flash on the dash and ROPS but turn signal switch & warning light switch was off.
Mine has A,B,C,D with four gears in each range and can be shifted without the clutch, also has a forward/reverse selector on the left side of the steering column that can also be shifted without the clutch. All I see is one filter underneath, I havent seen the other one but I do plan to change those, the one I see is original. The tractor only has 1050 hours.

I can remove the two fuses that having the transmisson sign (row F4) and put them back in and the tractor will move for a few second then stop and the selector goes back to N, then I can hit the hazard light switch and get it to work forward and reverse again for a few seconds. But even when it will move forward or reverse, the PTO or the rear hyrdraulics will not work.
 

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You must have the Power Quad w/Power Reverser transmission.
There should be two filters. One is a spin on. From JD parts it will be painted black. Original will be painted green, no markings. The second is an element that is in a housing.
It's near the right rear tire. JD recommends changing BOTH filters, not just one, and fluid at 100 hours then every 750 hours. There is also a sump screen that should be cleaned/checked after fluid is drained.


But your problems sound more electrical.


Have you pulled trouble codes? I think you can do that and read them on the dash. Pulling fuses may have deleted them? JD110 might know.
 

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Discussion Starter #8
You must have the Power Quad w/Power Reverser transmission.
There should be two filters. One is a spin on. From JD parts it will be painted black. Original will be painted green, no markings. The second is an element that is in a housing.
It's near the right rear tire. JD recommends changing BOTH filters, not just one, and fluid at 100 hours then every 750 hours. There is also a sump screen that should be cleaned/checked after fluid is drained.


But your problems sound more electrical.


Have you pulled trouble codes? I think you can do that and read them on the dash. Pulling fuses may have deleted them? JD110 might know.
What do you do see the codes? And I guess that filter has been changed because it is black.
 

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Do you have the owners manual? If so, look in section 130 Diagnostic Trouble Codes.
If not, you can view the owners manual online at JD web site.
 

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It does sound like you have electrical issues. THe symptoms you describe sound like CanBus issues. The CanBus is a pair of communication wires that the controllers "talk" to each other on. The system is composed of a twisted pair of green and yellow wires that should have about 2.4 and 2.6 volts on them. If voltages get out of range, communication gets scrambled. Voltages can get upset many ways. A short to ground or a short to 12 volts will do it as well as the green and yellow wires getting shorted to each other. A bad controller or a bad terminator can do it as well. On a 6420 the controllers are Instrument cluster, HCU for the hitch, CCU for the functions of pto and many other things, An ECU for engine, An RCU for reverser if equipped, and others are possible depending on how tractor is equipped. Another thing that can foul up the system is non John Deere accessories plugged into the CanBus. There is a round 9 pin connector behind the seat. Never plug anything into it to get power. No radios, lights, etc. This can be very complicated to diagnose. Recommend you talk to your dealer.
 

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Discussion Starter #11
The speed sensor or tach sensor was changed and did not fix the issue. An ex John Deere mechanic of 15 years could not find the problems either...
 
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