# John Deere 6400- Troubleshooting In-tank Fuel Transfer Pump Circuit



## landrand (Aug 22, 2004)

My John Deere 6400 (Product ID# L06400v131378) has been sitting in the garage for 5 years with no use. I am now taking the necessary steps to get it back in running condition.

1. I drained the fuel tank and put in 5 gallons of fresh diesel fuel.
2. I changed the fuel filter.

Unfortunately, I was not able to get the tractor to start. When troubleshooting the issue, I discovered my in-tank fuel transfer pump was not pumping fuel to the fuel filter when I turned the ignition key to on.

I removed the in-tank fuel transfer pump and tested it with a 12V battery. The pump was bad and I am preparing to replace it with a new pump/sending unit and new fuel lines.

When testing the wires to the sending unit/pump (with the ignition key on) I'm only getting 7.2V. I'm a novice to fuel transfer pumps so I did a little research. I read that fuel pumps often use various changes in voltage to control the flow of fuel. I suspect it should be 12V but am not sure. Have a couple of questions for the guru's:

1. Should the voltage to the pump/sending unit be a full 12V when the ignition key is on?

2. If 7.2V is low, I need to troubleshoot the circuit for a high resistance. I don't have the circuit wiring diagram but I suspect the ignition key switch, and fuse F101 Main Switch (Term BAT) are part of the circuit. Would anyone have a wiring diagram or information where I should begin troubleshooting this circuit with an multimeter?

Any advice/recommendations to this issue would be greatly appreciated!


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## oletrapper (5 mo ago)

Good morning Landrand,
I'm not a guru but I believe the voltage for the pump motor should be 12v. The unit is also your fuel level indicator circuitry so there should be 4 wire connections. Make sure your metering the correct ones. If there are only 2 wire connections, someone may have been in there before you. :-( The fuel circuitry wiring will possibly be lower than 12v. There is also the possibility that JD runs everything in the fuel level/lift-transfer pump assembly on the lower voltage. Try it before you install. Submerge in fuel with fuel hose back to bucket, turn on the key. Good luck. Keep us posted.  OT
Sure wish I had a 6400 sitting around in my garage. lol :-(


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## landrand (Aug 22, 2004)

oletrapper said:


> Good morning Landrand,
> I'm not a guru but I believe the voltage for the pump motor should be 12v. The unit is also your fuel level indicator circuitry so there should be 4 wire connections. Make sure your metering the correct ones. If there are only 2 wire connections, someone may have been in there before you. :-( The fuel circuitry wiring will possibly be lower than 12v. There is also the possibility that JD runs everything in the fuel level/lift-transfer pump assembly on the lower voltage. Try it before you install. Submerge in fuel with fuel hose back to bucket, turn on the key. Good luck. Keep us posted.  OT
> Sure wish I had a 6400 sitting around in my garage. lol :-(


I did some more testing and this is what I think my In-tank Fuel Transfer Pump circuit design looks like. After performing a few voltage measuring tests, this is what I come up with. My issues seems to be that Pin 2 on the Relay is not getting 12V when I turn on the ignition key. Today, I'll do some troubleshooting on the connection between pin 2 on the relay to the ignition terminal on the key switch. Thanks for the help!


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