4X4 not working in a 2001 F350 Dually - Low Range Works - Diesel Forum - TheDieselStop.com
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99 & up 7.3L Power Stroke Engine and Drivetrain Discussion of the 99 & up 7.3L Power Stroke diesel engine and drivetrain in the 1999-Up Super Duty trucks and Excursions. No gas engine discussion allowed except on transmissions and drivetrain that pertain to all models. Please confine discussion of topics in this forum to those items that are specific to the 7.3L Power Stroke engine.

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Old 07-18-2006, 08:12 AM   #1 (permalink)
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4X4 not working in a 2001 F350 Dually - Low Range Works

Hello Guys,

I just bought a 2001 Ford F350 Crew Cab Dually Automatic 7.3 PowerStroke... with 4x4 on the fly.

The 4x4 is not working. The 4X4 light does come on in the dash but it will not engage. The 4X4 Low Range however does work fine.

Is this problem related to 4x4 relays? If so.. where are the relay's located. My owner's manual does not indicate the location.

Could it be the transfer case? is there any easy way to check the transfer case?

The transmission works great.

Thanks ! [img]/ubbthreads/images/graemlins/confused.gif[/img]
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Old 07-18-2006, 08:44 AM   #2 (permalink)
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Re: 4X4 not working in a 2001 F350 Dually - Low Range Works

check voltage or ohm out the transfer case electronic shifter (black wiper motor type thing on the side of transfer case) to see if the motor is bad.
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Old 07-18-2006, 07:10 PM   #3 (permalink)
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Re: 4X4 not working in a 2001 F350 Dually - Low Range Works

Just had a friend come over.... he told me the hubs were not locked in and that is the reason the 4x4 did not work [img]/ubbthreads/images/graemlins/shrug.gif[/img] sorry but i am new to the 4X4 thing... [img]/ubbthreads/images/graemlins/rolleyes.gif[/img]

Thanks for the info though.
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Old 07-18-2006, 08:27 PM   #4 (permalink)
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Re: 4X4 not working in a 2001 F350 Dually - Low Range Works

You don't have to put the hubs on "lock" for the 4wd to work. They should be in "auto" and when you shift the switch on the dash they auto engage. You need to keep trouble shooting.
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Old 07-18-2006, 08:53 PM   #5 (permalink)
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Re: 4X4 not working in a 2001 F350 Dually - Low Range Works

Since you are new to 4x4's maybe it is working and you just don't know.

I'd say check your vacuum lines (since you have the 4x4 on the fly and not on the floor) because they are opperated by a vacuum whereas the low range I do believe is electrical. This would explain why 4x4 doesn't work but the low range does.
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Old 07-14-2011, 02:42 PM   #6 (permalink)
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I have kinda the same issue but mine the low didnt work and now the high is gone as well. Is the vacume box behind the passanger side batt? I now have a funny noise kinda like a buzzing noise that comes from it. Sometimes when I try to enguage it the AC dosent blow out of the vents but the defrost section.
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Old 07-14-2011, 03:50 PM   #7 (permalink)
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Quote:
Originally Posted by huntin76 View Post
I have kinda the same issue but mine the low didnt work and now the high is gone as well. Is the vacume box behind the passanger side batt? I now have a funny noise kinda like a buzzing noise that comes from it. Sometimes when I try to enguage it the AC dosent blow out of the vents but the defrost section.
Here's a quick rundown on how the system works.

The switch on the dash controls the electric transfer case motor and a vacuum hublock solenoid that controls the vacuum operated hubs.

Starting in 4x2 position, the transfer case is disengaged, and the hubs are unlocked.

When you move the switch to 4 HIGH, the relays start the motor on the t-case and shift it, stopping when a switch on the motor indicates it's in the right position. The "4x4" light on the dash turns on at that point. At the same time, a voltage signal is sent to the vacuum hublock solenoid for a certain pulse length, which applies vacuum to the hubs to lock them.

When you move the switch to 4 LOW position, the relays start the motor (moving in the same direction) to shift the t-case to low range. Again, the position switch stops the motor when it reaches the proper spot and the "LOW RANGE" light comes on. Nothing happens with the hublock solenoid, as the hubs should already be locked.

Moving back to 4 HIGH, the relays start the motor in the opposite direction and the t-case moves back to 4 high position, and the "LOW RANGE" light goes off. Again nothing happens with the solenoid, because the hubs need to stay locked.

Moving the switch to 2WD, the relays start the motor, again in the reverse direction, and the t-case moves back to 2WD position, the position switch on the motor stops it and turns off the "4X4" light. At the same time, the solenoid is signaled to send a vacuum pulse (either shorter or longer pulse than locking - kind of like a ball point pen button) to the hubs to unlock them.

The OP's saying that 4 HIGH doesn't work and 4 LOW does is either incorrect or something is really messed up in the controls, as the hubs stay locked between 4 HIGH and 4 LOW. Maybe he was just seeing the "LOW RANGE" light and mistook being in 2 LOW (hubs unlocked) for actually being in 4 WD.

On your specific problem, the buzzing behind the passenger side battery is the vacuum pump trying to keep up with a vacuum leak. No vacuum will default the HVAC to blow out the defrost vents. So you need to track down where there might be a vacuum leak. Start by disconnecting and plugging the lines coming from the pump and heading either to the cab or toward the hublock solenoid. If the pump stops then, the line you plugged has a leak downstream from where you disconnected it. Common spots are the vacuum lines to the hubs, the hublock solenoid itself, or someone had stuck their feet under the glove box and pulled a vacuum line loose there. Since your AC goes to defrost when you try to shift into 4x4, the leak is probably on the hublock tubing circuit.
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Last edited by klhansen; 07-14-2011 at 03:54 PM.
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Old 07-14-2011, 09:29 PM   #8 (permalink)
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Excellent explanation!

The only thing I would add is to say that the vacuum pump will run for several seconds after the leak is plugged, due to the need to fill the reservoir. I was rather surprised at how long it took the first time I had to let mine fill from empty. So be patient in your testing.

Also, the OP needs to understand the hub control positions and factor that into his analysis. Manual locking is achieved by turning the control clockwise and this overrides the need for the vacuum system to be functional. The automatic position (counterclockwise) depends on the vacuum to lock the hubs, and probably will not succeed if there is vacuum leak. If the HVAC moves to defrost upon activating the dash switch, it means the vacuum leak is probably either in or after the solenoid.
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Old 07-15-2011, 08:42 AM   #9 (permalink)
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right on guys thanks for the info. I did find a leak on the hose going to the hub. I still have no 4x4 0n high or low. I know that you can turn the hub to manual but I got this truck in 2003 (its an 01) and I have NEVER been able to turn them by hand. Thanks for the help now where should I start looking now???
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