Oil & Fuel John Deere 4120 Thermistor Location

kprei · Nov 4, 2011

I have a 2007? JD 4120 that will not start. I'm fairly sure it is the thermistor but I am having trouble finding it. I removed the fuse box but it is not located on the back of the fuse box. Does anyone know exactly where it is located on this tractor. I have a service guy coming next week but I would rather do it myself.

beenthere · Nov 4, 2011

:welcome:
I presume you have done a search for that location and it isn't showing up.

If not, maybe this schematic in post #2 will give you an idea, presuming the 4120 is similar.

http://www.tractorbynet.com/forums/john-deere-owning-operating/181040-thermistor-replacement.html

And a search on "Deere thermistor" may give you more info.

RoyJackson · Nov 4, 2011

I hope that link BeenThere posted helps, but wiring harnesses change quite a bit...however, checking the fuses and relays may be of help.
That diagram is for the older 4x00 and 4x10 tractors built from 1998 to 2004-2005.
As far as the thermistor location...IF it's used on the newer 4x20 series tractors..good question for your dealer (before the tech comes out). Also, a good time to consider purchase of a Service Manual for the 4x20 series tractors, eh?

kprei · Nov 4, 2011

I actually printed out that same skematic and pulled the fuse box but the only thing behind the relays are 4 or 5 wires running into the back of the fuse box where the relays plug in. I see little red plastic pieces next to the wires but I assume they are what hold the wire. I wish I had a picture I could post but I am at the office now.

Glen Watkins · Nov 4, 2011

What do these thermistors do and anyone know if they are on the 4x20 series?

shadog1962 · Nov 7, 2011

Glen Watkins said:
What do these thermistors do and anyone know if they are on the 4x20 series?

I was told by my dealer they supply a higher voltage to the fuel solenoid during starting then backs off to run voltage after the tractor has started. I was having trouble with my 4200 not starting. I actually replaced the fuel solenoid and it worked okay but since this was an intermittent problem it came back. I returned the solenoid and got a thermistor, problem solved. I don't remember what the voltages were I just know they are different from start to run. It is a common problem I guess. When I took the fuse panel out I found the leads for the thermistor had already been replaced once. I bought a spare thermistor they are only a couple dollars. I will put longer leads on so I don't have move the fuse panel anymore.