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My neighbor has a Jogn Deere 6420 with powerquad plus. it has 4 manual range gears (A,B,C,D) and has an electric toggle switch that controls 4 gears in each range. I was planting a few months ago and was on a long pass, and all of the sudden the tractor surges forward. the transmission powerquad light(gear) is flashing and i no longer have the electric gears. the manual range gears work fine but the electric gears seem to be stuck in 4th gear. the numbers went away for the electric gears on the dash, so it feels based on speed that im in 4th electric gear. what happened?

i am not familiar how to pull codes since this isnt my tractor, and i looked up how to do it and was confused. anybody have any ideas. ive looked for countless hours on the issue without luck. we continued planting and using it to this day without electric gears.

could a solenoid for the elctric gears came unplugged or solenoid gone bad? any cluses would be great. thanks!!
 

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Wild guess; did you lose ground speed indication on the dash? Maybe the ground speed sensor failed and the control unit for the power quad plus, does not "know" how fast the tractor is moving so it will not allow gear shifts???
 
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You should have 2 switches to operate 1-4 gears. The rocker switch on the right console and rabbit and turtle buttons on the ABCD lever knob. I have seen the buttons in the ABCD lever get stuck and cause this issue. Might need to replace that switch in the handle. Also have seen the wires leading to that switch break at the bottom of the lever where the wire bends constantly when shifting the range lever. Could be other problems but they are the most frequent I have seen. If someone could read the codes for you, it will point you in the right direction.
 

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i will try to get codes. im sure its fairly simple to find codes but the instructions looked ridiculous. the buttons on the joystick are gone. lol. this guy is rough on his equipment. i was wondering if it was a wire somewhere along the undercarriage got disconnected because i was planting in a field with heavy onions, and wondered if an onion grabbed a wire and pulled it out. ill try to get those codes soon though.
 

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Wild guess; did you lose ground speed indication on the dash? Maybe the ground speed sensor failed and the control unit for the power quad plus, does not "know" how fast the tractor is moving so it will not allow gear shifts???
i did not loose my ground speed readout.
 

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i will try to get codes. im sure its fairly simple to find codes but the instructions looked ridiculous. the buttons on the joystick are gone. lol. this guy is rough on his equipment. i was wondering if it was a wire somewhere along the undercarriage got disconnected because i was planting in a field with heavy onions, and wondered if an onion grabbed a wire and pulled it out. ill try to get those codes soon though.
Time to crawl under it and look. JD sells a shield kit, sounds like it needs one.
 

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I have experienced numerous problems with my 6420 Power Quad Transmission. Solenoids shorting out, tractor acting very erratic with surging after the tractor gets warmed up when the shuttle is engaged. Very dangerous. Nobody in JD land ever came up with a viable solution until I said that it appeared that the electrical connection between the shuttle and the transmission was experiencing an electrical problem in that the current is not flowing correctly to the transmission to make the transmission shift properly and possibly was causing voltage changes to the solenoids which caused them to fail. Guess what, somebody finally listened and they discovered that the regulator for the shuttle was defective causing the problem much like you have described. I have had to determine which solenoid controlled the up and down shift within the four ranges and which ones control the forward and reverse shifting. The mechanics did not even know this information and by the way there is a master solenoid on the transmission that they tried to blame for the problem while it is not at fault causing the problem that I have described. You might also want to know that the solenoids can be tested with a volt meter and if they are good the resistance with be between 15.5 and 16. I am sorry to be the bearer of bad news but too many of the service departments have just morphed into parts changers without being able to diagnose the real problems to fix your equipment.
 
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