How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask mike Your Own Question
mike, Technician
Category: Heavy Equipment
Satisfied Customers: 112
Experience:  certified master tech 20+ years combines, row crop, and four wheel drive
Type Your Heavy Equipment Question Here...
mike is online now
A new question is answered every 9 seconds

I have a John Deere 6420 Tractor that is having major problems.

Customer Question

I have a John Deere 6420 Tractor that is having major problems. It all started with a flashing warning on the dash that said load depth control is defective. At the same time the tractor would not shift by the shift button and the lights would not work. Now the lights started working but the tractor quit pulling. when i push the lever forward or backward to move it only beeps. i do not see any loose or broken wires. i dont understand why everything went crazy all at once at different places.
Submitted: 7 years ago.
Category: Heavy Equipment
Expert:  mike replied 7 years ago.

Hi could I get a little more info, are there any code . Is this a cab tractor or A rops tractor.

thanks mike

Customer: replied 7 years ago.

Yes Mike there are some codes that are showing. I understand about your harvest time the farmers around here (mississippi) are so far behind and we got another rain last night.

The tractor is a cab and air MFWD

I went thru the whole system and here is what is going on.

When we cranck the tractor a message pops up saying - defective load depth control

code 303053 - 4 bcu

when i turn on the pto it says to sit on the seat or turn off pto - code 302077 - 4bcu

when i turn the flashers on - code 302131 - 31 bcu

the lights quit working then started again

air and heat works

mfwd works

we were clipping our pasture yesterday and the whole dash started flashing on and off then about an hour later the tractor stoped. i pulled the reverser back and it backed up approx. 20 feet and stoped moving again. when i try to go forwards or backwards it beeps as if i have it in park or i have gotten out of the seat with the pto on. i have had several tractors and equipment and understand the mechanics of everything but this one has me puzzled. it has to be electrical but i dont know where to start other than replacing the load depth control. but would this cause everything to go haywire?


Expert:  mike replied 7 years ago.

Hi ok the first thing we might check is the seat switch. at the back of your bottom cushion there is a 2 pin {or wire} plug. unplug this plug check continuity at the seat switch {under the cushion} it should be open if you are not in the seat. Now sit in the seat and you should have continuity. If you don't check this a couple of times to verify and then replace the seat switch.


Next I am going to tell you how to get into technician mode on your display. We will need this to pull all the codes and to check voltages on load and depth. turn the key switch to off position. Now turn the key switch on and within 1 second hold down on the rms switch until the display changes to dia. { the rms switch is the little lever under the steering wheel} when you in dia turn your signal light up or down until you see all. when you see "all" turn the hazard warning switch on then off. write down all these codes with all their numbers and control unit ie bcu ecu ect ect. when clear appears on the display you can cycle { on then off} your your hazard light switch and this will clear them.


after you have done this turn your key switch off, then once again enter into tech mode as previously explained. This time turn your signal light switch until you see bcu. cycle your hazard light switch, this will enter us into this control turn your signal light switch until you reach bcu 106 , now turn your hitch sensitivity potentiometer full counter clockwise voltage should be between 0.25-1.5 then turn you knob clockwise full and it should be3.5-4.75 volts on your display. If no voltage is is shown you have a wiring problem if voltage is out of spec your potentiometer is bad.


we will start here if you have any problems I will try to reply back to you around lunch time. please let me know all the codes and what the other 2 test show.



thank you , also don't click accept until we have found the problems



Edited by mike on 10/28/2009 at 11:37 AM EST

Related Heavy Equipment Questions