Hello,

I am new to these forums, not new to Ford trucks, but this is my first diesel . I just traded in my trusty, never had a single issue 2008 Ford F150 with 53k miles for a 2008 Ford F350 with 112k miles. I figured the extra miles were okay, because it is a diesel. I purchased the truck to pull a 31’ 12k lbs when loaded toyhauler, and I have a 14K weight distribution hitch.

Just in case this makes a difference, here is some background information before I explain what I need help with. I have a 2008 Ford F350 XLT 6.4L CrewCab Long Bed. Before purchasing it, I had Ford do a performance and safety inspection. Everything came back clear, so I bought it. The day after purchasing it, I changed all the fluids for peace of mind, ie. rear diff, transfer case, transmission, motor oil & filter, fuel filter, and radiator fluid.

Here is the problem. Occasionally, the 4x4 Low light will start blinking/flashing. Sometimes it will only flash once or twice and go off, other times it will flash for 15-20 seconds and then go off. There is no pattern to when it happens other than it seems to do it mostly when slowing down or breaking. It is very sporadic. I don’t drive very far for work, so I can go an entire week without seeing the light come on, but if I hit the highway for 30-45 minutes, the light will eventually turn on.

When it flashes, occasionally, I get an RPM increase…almost like it’s trying to engage natural or shift into 4x4 low at highway speeds…which causes me concerns. I took it to Ford and after 50 miles of driving it around, they could not get the 4x4 low light to come on. They said they pulled codes but there were none to pull. They reflashed the PCM and charged me $99 to not fix my problem.

I can shift into 4x4 high and 4x4 low (with the window rolled down, I can hear the shifting from 2wd to 4wd high and then to 4wd low and back to 2wd), so I don’t think it is a blown fuse or the control module. I removed and cleaned the wire connectors to the shift motor on the transfer case, and that didn’t fix it. I was thinking about replacing the rear diff abs speed sensor in hopes that will fix it. I think that maybe it’s a wiring issue, which I wouldn’t even know where to start. However, does anyone have any suggestions as to what it could be before I start throwing a ton of money at it. It’s really discouraging that I took it to Ford and they didn’t do any for me, infact they made my mpg worse.

I was getting 14 mpg before the reflash and after, I am now getting 8 mpg. Does this seem right? Or is there a learning period after a reflash before my mpg gets back to normal.

Also, the automatic 4x4 drive doesn't work. I don't think its holding a vaccum. I don't think it is related to the 4x4 low light coming on when I am doing normal driving. I can use the lockers to get 4x4 to work correctly. Infact, Ford is the one that told me the auto doesn't work.

Edit: I also noticed that if I flip ON any of the upfitter switches (ie AUX 1, AUX 2, AUX 3, AUX 4) the 4x4 low light will flash constantly until turned off. I currently don't use any of the switches for anything.

 

Ordered the speed sensor. It will be here on Tuesday. Fingers crossed that it corrects the issue.

 

Very odd symptoms. Let us know if the speeed sensor helps.

 

The rear differential speed sensor came in today. I swapped them out, but I still have a blinking 4x4 low light.

I'm somewhat clueless at this point as to what could be causing the problem. I am going to replace the 4wd shift motor and see if that works. I'll keep you posted. Feel free to share ideas, if you have any.

 

The only thing I have been able to locate concerning a 4x4 light states:

The 4WD system indicator lights illuminate only under the following
conditions.

They discuss 4H, 4L.

If these lights illuminate when driving in 2WD, contact your
authorized dealer as soon as possible.

Not real helpful

 

Almost sounds like an intermittent ground, especially with the information about the upfitter switches. Maybe check the ground connection for the upfitter switches and dash.

Just a thought. Good luck.

 

I am starting to see a pattern when the 4x4 Low light flashes. It seems to happen after the truck has reached normal operating temps (doesn't seem to happen when the truck is cold). Also, 85% of the time it comes on, I'm either braking or slowing down. Any ideas why it is happening under those two conditions.

Ford suggested replacing my transfer case shift motor because the contact plates "could" be going bad. However, the truck has no problem shifting into 4H or 4L. Could it really be the shift motor?

 

 

Any updates? This is exactly what is happening to my 08 f350. I also have to manually lock in my hubs to get them to engage and the light blinks sporadically. I occasionally haul my dump trailer it acts up really bad when I do that. Please let me know if you came up with a fix, everyone else I see says they ended up trading it in....
thanks