John Deere Fuel Gauge Failure Cause

[glcaines]

I have a 2003 JD 5520 cab tractor that the fuel gauge quit working on about 5 years ago. I replaced the sender and no change, so I've lived with it since. I also have a 2000 JD 4600 that I've had since new. Last week, the fuel gauge quit working with the same symptoms as the 5520. The sender is OK. The symptoms are that the fuel gauge needle swings around, sometimes pointing straight down and the position has nothing to do with fuel level. Replacement instrument clusters are very expensive. I understand that this is a fairly common issue with some JD tractors. Has anyone actually diagnosed what component actually fails in the fuel gauge? Perhaps it is possible to repair the instrument cluster without replacing it. All of the other gauges on both tractors work fine.

 

[lpakiz]

Try rigging up a temporary ground from the negative battery post to the base of the fuel sender itself.
I have seen a fuel tank lose its ground to the frame.
i was a truck mechanic for quite a few years. Senders fail, wiring fails, the ground path fails, but the dash gauge VERY VERY seldom fails.

The sender itself is no more than a " variable ground" device, but whatever ground level it produces,must eventually be forwarded to the negative battery post.

OR, If you can access the gauge and ascertain which wire comes from the sender, (variable ground) and which wire is 12 V+ supply, you could wire a temporary, external, parallel ground wire from the non supply (ground) side of the gauge to the sender. That might indicate a broken or otherwise non-functional wire or connector somewhere between the sender and the fuel gauge.
I have, on occasion, removed the sender from the tank, grounded it and then moved the sender arm manually as I watched the gauge.

 

[Roadworthy]

That's all very good troubleshooting information. I don't know John Deere specifically but I do know many vehicles use a printed circuit board or that type conductors for their instrumentation. If you can access the dash look for broken traces and cold solder joints. These can be easily repaired.

 

[glcaines]

Try rigging up a temporary ground from the negative battery post to the base of the fuel sender itself.
I have seen a fuel tank lose its ground to the frame.
i was a truck mechanic for quite a few years. Senders fail, wiring fails, the ground path fails, but the dash gauge VERY VERY seldom fails.

The sender itself is no more than a " variable ground" device, but whatever ground level it produces,must eventually be forwarded to the negative battery post.

OR, If you can access the gauge and ascertain which wire comes from the sender, (variable ground) and which wire is 12 V+ supply, you could wire a temporary, external, parallel ground wire from the non supply (ground) side of the gauge to the sender. That might indicate a broken or otherwise non-functional wire or connector somewhere between the sender and the fuel gauge.
I have, on occasion, removed the sender from the tank, grounded it and then moved the sender arm manually as I watched the gauge.

I tried running the ground wire on both tractors and there was no change in behavior. My local JD dealer told me that it was a fairly common problem for the instrument clusters to fail, causing the problem and that the instrument clusters can't be repaired. However, I've seen companies on Ebay advertising that they can repair the JD instrument clusters, but the cost isn't cheap, although it is less expensive than a new JD instrument cluster. If I knew exactly what fails, perhaps I could repair it myself.

 

[lpakiz]

A couple more tests.....

Can you UNHOOK the wire from the sender and leave it dangle ungrounded? (Key ON)
Does that change anything on the dash gauge?

Do you have a digital voltmeter? Can you detect voltage on the unhooked sender wire? Should be something there, but not necessarily 12 volts. Some systems used 5 volts, iirc.

Now, GROUND the sender wire to the negative battery post. (Again, don't trust the existing ground path--yet)

If the gauge doesn't react to either action (shows full or goes to empty) I would be somewhat more comfortable condemning the dash gauge.

Can you remove the sender relatively easily? If so, remove it, set the digital meter to OHMS and hook the meter to the sender terminal and to the sender base. Now manually move the float thru its range. You should be able to see the ohms change as you swing the float thru it's range. This works really well with an analog gauge, as the needle will sweep smoothly thru its range if the sender is good. I have found a faulty sender that showed a smooth sweep except for a small "blip" somewhere in the middle of the sweep, indicating a fault in the resistance winding on the sender, but in these cases, the gauge would sometimes show correctly at different, random, fuel levels.

 

[deserteagle71]

Must be a John Deere thing. My 2020 diesel is ~ 60 years old and the fuel gauge has never worked correctly. I've played with it through the years - put in new wiring, a new float/sender unit, etc but nothing helped. As I'm driving along the gauge mostly points at completely full but occasionally at empty or just somewhere in between. So for years now I just stick the tank when I figure it might be running low.