4X4 out? Start here!

[Truck3]

Well, after an exhausting search and destroy mission, I have learned a few things that I thought someone else could benefit from.
I had an issue where the dash indicator was showing the vehicle was in 4X4, but clearly it was not. I will walk you through the 2 sides of the system to help narrow down the problem in hopes you do not have to go through what i did to repair it. Here goes.......
With the vehicle running, turn on the Air Conditioning (A/C) controls with the fan set on high.
Switch the vehicle into 4H using the Electronic Shift on the Fly knob (ESOF). If the system changes over to defrost on its own, you have a vaccuum related issue. Crawl under the vehicle and with your hand try to spin the front drive shaft. If it is tight and does not spin, you have confirmed the issue lies within the vacuum system and the front hubs are not engaging.
If during this little A/C switch and ESOF test, the vehicle stays with the A/C on, you have an electro-mechanical issue with the transfer case.
If your vehicle passes the vacuum test and is still not in 4X4, again, crawl under and try to spin the front drive shaft by hand, it will spin. You have now confirmed the Electro-Mechanical failure with the transfer case.
There are 2 main components to the Electro -mechanical side of the transfer case.
1. The transfer case control module (TCCM)
2. The Transfer case shift motor(TCSM)
These two units are linked together. The TCCM takes information from the ignition computer and the wheel speed sensors and controls the shift motor to engage or disengage the transfer case.
According to the Ford dealer who has a single tech solely dedicated to 4x4 systems.......
If the TCSM fails due to a component failure, it will fry the TCCM. Plain and simple. The motor failure in most cases sends voltage back to the TCCM and turns it into garbage.
He also stated that there is no way for a bad TCCM to ruin a TCSM. So, this is a one way street.
If I have not bored you completely by now.........
Computer diagnostics will be able to indicate if the TCCM is bad. Remember, that electronic parts are only made for 7 years after the date of manufacture, and therefore, you may be reliant on used or NOS parts.
Having the right TCSM is critical. Ford used several different wiring configurations on the truck line, All with good reason. You MUST make absolutely sure the Transfer case motor you purchase is a direct replacement for yours. The Style of the plug, and the number of wires is critical. one bad step here could cost you a Control module, like it did me.
If you have isolated the issue to be on the Electro-mechanical side of the system do this test next.
With the vehicle running and in park, crawl under and place your hand on the Transfer case shift motor. Have someone in the vehicle engage the ESOF knob to 4H. If you feel the motor run briefly, it is good, the problem may lie in the control module.
If you do not feel the motor engage through light vibration of the motor case, you have a bad shift motor.
Try replacing the shift motor first, change the transfer case fluid while you are under there and about 80% of the time, this will do the trick. If it does not.....the only other component is the Control module.
The ford Tech tells me that in less than 10% of the vehicles actually need some other work done on the transfer case itself.
I hope this helps someone else on here at least get a start as to where to go on figuring out why you have no 4x4.

 

[1955moose]

That was a great explanation. You work like I do with common sense and easier diagnostics of vehicle problems. You guys out there reading this take notes! Class is over!


Sent from my iPhone using Tapatalk

 

[RedExpy]

wow

holy Crap!!! I hope I never have to go through that... but thanks for the write up!!!! well done and appreciate the insight!

 

[Truck3]

Glad you all liked the write up. It was the simplest way for me to describe what i found. As i get older, I have the 250-8 rule......
I'll throw $250.00 and 8 hours into an issue before deciding to take it in. Obviously there are routine maintenance items that exceed the 250, but in general, there is a point where If i am unable to figure out what the problem is, there seems no point in throwing more parts at something just by guessing.
I am fortunate to have a competent ford dealer in my area that I trust. It only happens about once every 4-5 years that I end up having to take something in. When it happens, I figure i am still on the winning side based on what I saved over that 4-5 years in doing the work myself.
I have found that the advanced computer diagnostic equipment available at the dealers have made the problems much easier to diagnose and in turn, saves on the labor charge.
Fore most other jobs, I'm a big proponent of DIY.

 

[1955moose]

Your 250-8 rule is similar to when I ran a Harley Davidson repair/rental years back. I would tell customers H/D stood for hundred dollars, that's what it took minimum to put on lift! They usually laughed breaking any first time tension.


Sent from my iPhone using Tapatalk

 

[laketrash]

Excellent write up and great rule!

I'm exiting the diesel world to come back to gas engines because I was hitting the 250/8 too often. My guess is it was more my experience level in diesels than anything else. Problem I ran into once I was ready to take it somewhere was finding a diesel tech that had true mechanic skills.

So I just traded my F250 in on a 4x4 Expedition and reading through this forum for issues and solutions so I'm prepared when they come up. Book marking this thread!

Thanks for your time to input this one!

 

[Goats]

From my understanding the transfer case motor only shifts from 4wh to 4wl and not from 2wd to 4wd

 

[Truck3]

You bring up an interesting question, but based on what I have learned the hard way, not completely accurate. But in theory, partially correct.
The TCSM rotates a shaft within the transfer case. It rotates the shift linkage in the case to match up the proper gears to the output shafts.
When the input from the ESOF is placed in 4H, the motor turns enough to engage the first set of gears that results in the spinning of the front drive shaft.
When the ESOF is placed in 4L, the TCSM moves into position 1, pauses for you to place the vehicle in Neutral, and continues to turn the shaft engaging the second set of gears for 4L.
The TCSM now tells the main engine computer to set rev limits based on the requirements for 4L.
Think of the input shaft of the transfer case as a worm gear essentially. It may ony take a few revolutions to line up the gears for 4H, and a few more to engage the gears for 4L.