4wd not disengaging on John Deere 6220

[Alms87]

Here's my situation. The voltage at the solenoid is about 8v regardless of switch position and is not enough to release the front wheel drive. The 4wd annunciator light is not on unless break is pressed or switch is engaged. Voltage at the switch is 14v when switched off and 0v when switched on. Also 14v at the fuse. So I either have a bad wire going to the solenoid or
some other electrical component between the switch and the solenoid. Does anyone know how this is wired up? I am considering running a separate/new wire from the switch down to the solenoid. Has anyone tried this? Thanks for your help!

 

[Zebrafive]

Wired so voltage goes to 4wd switch and then to 4wd solenoid when 4wd is "OFF". So solenoid should have 12+ volts when 4wd switch is "OFF".
When 4wd switch is "ON" voltage is switched to the dash light and no voltage should go to the solenoid.


So you need to determine why you have Only 8 volts at the solenoid and 8 volts at all times. Low voltage sounds like loose connection or bad ground.
Are you checking the solenoid voltage with it connected? Or at it's connector, but disconnected?
If you find 12+ volts to the connector for the solenoid with it disconnected, I would guess the ground wire out of the solenoid is the problem.

If you disconnect the connector at the switch, what voltage do you have at the solenoid?
What voltage at the wire (that would be from the switch to solenoid) with the switch connector unplugged from the switch?


My first guess is bad ground or connector at the solenoid. My second guess is another wire(s) is shorting to the power wire to the solenoid.

 

[Alms87]

Wired so voltage goes to 4wd switch and then to 4wd solenoid when 4wd is "OFF". So solenoid should have 12+ volts when 4wd switch is "OFF".
When 4wd switch is "ON" voltage is switched to the dash light and no voltage should go to the solenoid.


So you need to determine why you have Only 8 volts at the solenoid and 8 volts at all times. Low voltage sounds like loose connection or bad ground.
Are you checking the solenoid voltage with it connected? Or at it's connector, but disconnected?
If you find 12+ volts to the connector for the solenoid with it disconnected, I would guess the ground wire out of the solenoid is the problem.

If you disconnect the connector at the switch, what voltage do you have at the solenoid?
What voltage at the wire (that would be from the switch to solenoid) with the switch connector unplugged from the switch?


My first guess is bad ground or connector at the solenoid. My second guess is another wire(s) is shorting to the power wire to the solenoid.

Thanks Zebrafive! My solenoid measurements were at the solenoid connector with it disconnected from the solenoid but I did not measure it when the 4wd switch was disconnected, I will try that today.

Also here's something interesting. My brake lights do not work. Running lights work and turn signals both work, but brake lights do not. Brake fuse is good and brake fuse terminal goes to 14v when either brake is applied and 0v when not applied. I have read that brake light problems can lead to 4wd problems. Does this help getting to root cause?

 

[CobyRupert]

You also mentioned that some dashboard 4wd indicator would only light when brake pedal was pushed.
I think this is significant.
Some wires rubbing?

P.S. When indicating voltage, please note the two locations you are measuring across. Are all your voltages referenced to the frame, or neg post of battery, or across the device you’re measuring?

 

[LouNY]

Your brake light circuit could be intertwined with your 4wd,
many tractors will engage 4wd when both brake pedals are used.
Those circuits monitor the individual brake pedals so they do not activate the 4wd when just one brake is used but do activate when both pedals are used,
many times there is also a speed switch involved in that you need to be above 5-7 mph for the brakes to activate the 4wd.

 

[Zebrafive]

You also mentioned that some dashboard 4wd indicator would only light when brake pedal was pushed.
I think this is significant.
Some wires rubbing?

P.S. When indicating voltage, please note the two locations you are measuring across. Are all your voltages referenced to the frame, or neg post of battery, or across the device you’re measuring?

Brakes active 4wd for increased braking (having front wheels engaged)

 

[Alms87]

All measurements have been to chassis ground. The 4wd annunciation light that comes on when I apply both brakes is correct operation as 4wd is used to assist in braking.

 

[Zebrafive]

Thanks Zebrafive! My solenoid measurements were at the solenoid connector with it disconnected from the solenoid but I did not measure it when the 4wd switch was disconnected, I will try that today.

Also here's something interesting. My brake lights do not work. Running lights work and turn signals both work, but brake lights do not. Brake fuse is good and brake fuse terminal goes to 14v when either brake is applied and 0v when not applied. I have read that brake light problems can lead to 4wd problems. Does this help getting to root cause?

IIRC the brake pedals have switch for brake lights. I am not sure, but think the brake light switches send voltage to a controller that in turn powers the brake lights and cuts power to the 4wd solenoid to engage 4wd. Maybe the controller has loose connector(s) or broken wire(s).

 

[Alms87]

Still 8v at solenoid with switch disconnected and with the fuse removed. I really need the wiring schematics. Is it really $800 to buy the repair manual???

 

[Zebrafive]

This is sounding like a controller issue. IIRC JD calls it a BCU; Basic Control Unit.
You might try disconnecting BOTH battery cables and both ends of the ground cable and cleaning the connections. Bad grounds cause a LOT of problems. Having the battery completely disconnect will let the power "drain" from the controller(s) and reconnecting will "reboot" them.
Good Luck.
Have you tried to check for error codes?