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Figured I'd post this as a reference so that I can avoid typing the same answer again and again when someone has a 4x4 problem and they don't know where to start.
First, a system description: On the 2004 (new body style) and up F-150 Ford went to a new design for the 4x4 system. Each front wheel has a vacuum actuator, called an Integrated Wheel End. These IWEs are bolted to the inside of the steering knuckle by 3 bolts, and a half-shaft (front axle) passes through each one into the hub, which is on the other side of the steering knuckle and secured with 4 large bolts. These IWEs (sometimes also called actuators) are controlled by vacuum. This vacuum comes from the engine.
When your engine is off, there is no vacuum supply. However, vacuum is still stored in a vacuum reservoir which is located behind the battery. This is possible because there are two check valves in the vacuum lines. One check valve is between the vacuum tap on the engine side and the IWE Solenoid, and the other is in this same line (T- fitting in between) between the IWE Solenoid and the vacuum reservoir. These are on the vacuum supply side of the solenoid.The vacuum control side of the solenoid goes directly to the IWEs.
Now, this stored vacuum is not used when the engine is off, because the IWE solenoid (located high on the firewall aft of the battery) is not energized, and so vents vacuum in the lines that go to the IWEs. The purpose of the check valves, then, is to ensure an adequate supply of vacuum to the system even when the driver commands full throttle, which would normally also deplete the engine vacuum supply. This will become important in diagnosis later on. With no vacuum to the IWE, a spring forces a geared locking collar outward onto the hub gear, which then locks the hub and half shaft together.
With the engine running, there is an ample vacuum supply. In 2WD, the IWE solenoid is energized (grounded by the 4x4 control module, actually) and supplies vacuum to the IWEs. A vacuum diaphragm in each IWE overcomes the spring that would otherwise force the locking collar onto the hub, pulling the locking collar in and off the hub gear, which lets the hub spin and the half shaft remain stationary, thus unlocking the front wheels.
Ford went to this "hub disconnect" system for a couple reasons. First, it prevents the half shafts, differential, spider gears, and front driveshaft from turning as you drive down the road in 2WD, unlike systems from GM and Chrysler that use a differential or half shaft (in the middle of the shaft) disconnect. This saves wear on all these parts. It also saves some fuel, especially in stop and go traffic, since you no longer have to spin all those heavy parts up every time you accelerate. Speaking of acceleration, turning all those heavy parts costs you performance, so it makes sense to avoid it if you can, which the Ford system does nicely.
In addition to the IWE disconnect, there is also a Transfer Case disconnect. Without getting into the specifics, Ford uses a clutch and magnet to engage or disengage the front driveshaft in the TC. A Transfer Case Motor is used to move the range select lever in the TC from 2WD to 4Hi to 4Low. The TCM is just there to perform the function of a floor shift level, basically.
So, in 2WD, nothing in the drivetrain (front driveshaft, differential, half shafts) spins at all. When you turn the ESOF switch to 4Hi, a couple things happen simultaneously. First, the TCM moves the lever in the TC to the 4Hi position. This engages the front driveshaft, with the internal TC clutch spinning it, the differential, and the half shafts up to speed very quickly. This is partly why your manual says you must be below 55 MPH to "Shift-On-the_Fly". That's a lot of mass to spin up in a very short time. Second, the IWE solenoid is de-engergized (no longer grounded by the 4x4 module). This vents vacuum from the IWEs. Their springs then force the locking collars onto the hub gears, locking the half shafts to the hubs and, by default, the front wheels. Thus, with the TC locking the front and rear driveshafts together and the IWEs locking the half shafts to the front hubs/wheels, you have 4WD. Now, the IWE and hub gears also have to mesh up very quickly, all while the half shafts are spinning up to speed- another reason Ford says this must happen below 55 MPH.
In order to get into 4Low, the truck must be below 3 MPH with the transmission in Neutral (not Park, it has to be Neutral) and the service (foot) brake applied. The TCM moves the TC lever again, which changes the gearing inside the TC and locks front and rear driveshafts into Low range.
Now, you will notice that from the IWE's perspective, engine off presents the same conditions as 4Hi and 4Low- that is there is no vacuum supply and thus the IWE locking collar springs lock the half shafts and hubs together. You should be able to test the signal to the IWE solenoid from the 4x4 control module with a digital volt meter. Unplug the electrical connector. In 2WD (and when the engine is running) there should be voltage across the wire harness side terminals. In either 4x4 mode or whenever the engine is off, no matter where the ESOF switch is, there should be no voltage there.
Further, each IWE has two vacuum line connections. There is a double rubber vacuum hose at each IWE. You cannot put the hose on wrong- one hose is larger than the other. The larger hose is the vacuum control line from the IWE solenoid, and the smaller hose is a vent line that runs up high in the engine compartment and is not connected to anything (hence, it is only a vent).
Last edited by VTX1800N1; 12-31-2012 at 12:31 AM.
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OK, on to diagnosis. The two most common complaints are a grinding noise from the front end and general failure to achieve 4x4 operation.
So, we will begin with grinding noises. Most commonly, this is a result of a partial engagement of the IWEs on the hubs. Here is a YouTube video of what is supposed to happen depending on the vacuum state at the IWEs:
The wobbling part above is the axle half shaft, obviously cut away for this demonstration. The rubber accordion boot is the Constant Velocity joint, and next is the IWE which is bolted to the steering knuckle. On the far side is the hub with the hand crank attached, again for demonstration purposes.
If you have a grinding sound, whether in 2WD or when attempting 4WD, then one or both IWEs are somewhere between engaged and disengaged- not a good thing. It's possible that you only get the grinding noises on hard acceleration or when going up a hill (usually towing/hauling a heavy load) and I will talk about that a bit later. There are several different possible causes for this. The good news is that the system is fairly simple and so is easy to diagnose with few tools and little effort. Dealers charge an outrageous amount to diagnose and fix these systems and there is really no good reason for it. If you are out of warranty, do it yourself and save some serious $$$$$!
So, what causes a partial engagement of one or both IWEs? Ford has a TSB out about water getting into the IWE solenoid on early trucks with this system. The problem was that the placement of the solenoid put it directly into the path of water flow in rain conditions. Water can get into the solenoid and short it out. This can set some codes (follow the TSB link) and may cause the 4Hi and 4Low lights to be inoperative. This water can also get in the vacuum lines to the IWEs and make its way all they way to the IWEs themselves. Once water is in the IWEs, it can corrode the locking collar spring and freeze it in the engaged position, disengaged position, or somewhere in between.
Water can also infiltrate between the IWE locking collar and the hub. It can get in along the path of the half shaft where it goes through the IWE, between the IWE and the hub (there is a seal here that compresses slightly as the IWE is bolted to the steering knuckle), and through the hub seals or along the path the half shaft stub takes as it passes through the hub (there is a needle roller pilot bearing here). Water on this side mixes (not well) with the grease in the system and can corrode the IWE, Hub, or freeze in cold weather, preventing operation.
The hub vacuum seal can also fail. This usually results in an engaged (half shaft locked to hub) IWE on the problem side, and low vacuum on the other side. Thus, your grinding sound might be coming from the good IWE. This is bad because the problem IWE has to be replaced and if not fixed quickly will destroy the good IWE on the other side- requiring replacement of both. You can remove vacuum from the system by disconnecting the vacuum line before it gets to the reservoir (and depleting the stored vacuum in the reservoir by disconnecting the check valve) This will lock the half shafts in 4x4 mode and won't hurt anything because the TC is still unlocked, but might stop the grinding of the IWEs and hubs. This is somewhat of a design flaw in the system that allows this- both IWEs get their vacuum off a single line from the IWE solenoid.
Owners have also experienced vacuum lines that contacted hot exhaust components and melted, or broke, or got a hole worn in them from vibration. A few have also had the vacuum lines at the IWE pulled off for whatever reason.
I suppose it's possible for the vent line to get clogged and cause problems with IWE spring collar movement, but I've never heard of it.
About failed IWE positions- there are 3:
1. Engaged isn't good, because you are then spinning the half shaft and all attached parts unnecessarily.
2. Disengaged is worse, because the front differential is open. This means that when you want 4WD, it will not work at all if just one of the two IWEs does not engage. All the power will go to the half shaft that is not locked to the hub, and although the front driveshaft and both half shafts will spin, you will get no pull from the front wheels.
3. Somewhere in between is the worst case, because the IWEs are either trying to engage or disengage, and so the gears on the locking collar and hub are grinding themselves into oblivion. The IWE gears are softer, and so they take most of the damage (good thing too, as the hub is much more expensive).
Last edited by VTX1800N1; 12-31-2012 at 12:01 AM.
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So here is the obligatory legal disclaimer: Some people are simply not built to work on any mechanical thing, especially something as complex and heavy as a motor vehicle. Do not attempt any diagnosis or repair you are not completely comfortable with. YOU assume all responsibility and liability for performing any service on yours or any other vehicle. I hereby disclaim any and all responsibility or liability for any actions you undertake as a result of reading this How-To.
Ok, now that that's out of the way, let's get down to business. In order to check the system for proper operation, we will need to lift at least one front wheel off the ground at a time. You will need a jack with enough capacity to lift one of the front wheels. Check your vehicle sticker in the driver's door jamb for front axle weight. The truck should be in PARK and set the PARKING BRAKE. Block the rear wheels if you have any doubt about the truck rolling on you. Jack one wheel off the ground. At no time should you get under a vehicle supported only by a jack, even if all the wheels are still firmly in place. You can jack under the lower control arm where the spring strut attaches to it or under the frame aft of the front tire.
This test requires only that you look far enough under the truck to see if the half shaft is turning. Now, with either front wheel off the ground and the engine off, ESOF switch in 2WD, spin that wheel while watching the half shaft. The half shaft should spin with the wheel. Remember, there should be no vacuum in the lines to the IWEs so the spring locking collar should lock the half shaft to the hub/wheel. There will be some resistance to spin, because the other half shaft should also be locked to the other wheel and cannot move because it's still on the ground. This means that you also have to spin the spider gears in the differential and the front driveshaft in order to spin the lifted wheel. This is normal. If the half shaft of the lifted wheel does not turn when you spin the wheel in these conditions, then you have found part of your problem. Your IWE has failed disengaged or the IWE solenoid is stuck sending a vacuum signal to the IWEs all the time (rare)- remember there is still a reservoir with vacuum even when the engine is off and a check valve between that and the engine that prevents the engine from bleeding it off.
If you can safely reach the double vacuum line to the IWE without getting under the truck, pull it off (otherwise set the truck frame on jack stands first). If you hear a sound of vacuum release, then at least part of the problem is in the IWE solenoid which is not releasing vacuum. Replace the solenoid, but continue with diagnosis. Test again by spinning the wheel and see if the half shaft rotates. If it didn't rotate before but does now, the IWE is likely good and the solenoid is bad. If it still doesn't rotate, you have either an IWE or hub or both on that side that is bad. I'll discuss later how to determine that. In either case, you will need to remove the IWE and inspect it and the hub.
Make sure the vacuum line is back in place over both nipples on the IWE (you can't put it on wrong, one line is bigger than the other so it only goes on one way) and start the engine. Repeat the spin test. The wheel should now spin easy while the half shaft remains stationary. If the half shaft spins with the IWE, then you have a problem with the IWE, the vacuum lines, the IWE solenoid, or some combination thereof. In 2WD engine running, there should be an adequate vacuum supply to the IWEs to disengage the spring collar from the hubs. If the IWE doesn't disengage, you should get a vacuum pump/tester to check the system. I recommend something like this:
. A healthy engine will produce at minimum 17" of vacuum at idle at normal operating temperature. It takes only 7" of vacuum to disengage a healthy IWE. Test the vacuum to the IWEs at the large vacuum hose. You can also test the IWE independent of the engine by attaching the vacuum pump to the large IWE nipple. It should hold vacuum with no leak down and disengage completely by the time you have pumped it to 7". If it fails either test, replace the IWE (inspect the hub first to make sure those gears are not ground down to nothing). It's not serviceable.
Repeat the process for the other side. Again, with the engine off and the ESOF in 2WD, the wheel should be locked to the half shaft through the IWE so that both spin together. Engine running, ESOF in 2WD, the half shaft should be unlocked from the wheel/hub. Engine running, ESOF in 4WD, the IWE should lock the half shaft to the hub. As you've guessed by now, every time you shut your truck off, the IWEs go into 4WD mode (but the TC doesn't, so the front wheels don't actually have any holding power when parked).
If you discover low vacuum at either IWE, you might have a problem with a leaking vacuum seal at the other IWE, a leak in one of the vacuum lines anywhere in the system (IWEs to solenoid, solenoid to vacuum reservoir, solenoid to engine vacuum tap), or (unlikely) low engine vacuum at idle due to an engine problem. Most likely one of your vacuum lines has a leak. You will have to follow them for their entire length and inspect. Some owners have found that one of their double vacuum hoses has come off at one of the IWEs, which causes a low vacuum and grinding in the other. They just pull off and are not held on with anything.
This should help you narrow down the location of the problem- Vacuum lines, solenoid, or IWE/Hub. There are other possible failures I'll talk about next.
Last edited by VTX1800N1; 12-28-2012 at 09:42 AM.
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Sometimes the TCM freezes up. This happens more often when the 4WD system is very rarely used. I suggest "exercising" the 4WD system at least once a week by switching the system through each range 2Hi, 4Hi, and 4Low. The IWEs get exercised every time you shut your truck off, at a minimum, but the TCM doesn't. There are two ways to tell if the TCM is working.
1. If you can get into low range when switched to 4Low, no matter if you actually get 4WD out of the front wheels or not, your TCM is working. You will know you are in low range because the engine will run up through the gears quickly but you will still be going very slow.
2. With the engine running, transmission in PARK, ESOF in 2WD, set the parking brake and block the rear wheels. Lift at least one front wheel off the ground and place the truck on jack stand(s). Look under the driver's side of your truck and locate the front driveshaft. It comes out of the TC and goes to the front differential. Being careful of hot exhaust components, reach up and try to spin the front driveshaft by hand. It should spin with little effort. The front wheel is lifted here because we are testing the TC, not the IWEs. If both of your IWEs were failed in the engaged position and both front wheels on the ground, you would not be able to spin the front driveshaft. If you are sure your IWEs are disengaging in 2WD, engine running, then there is no need to lift the truck for this test. Next, switch the ESOF to 4Hi. Try to spin the front driveshaft again. It should not spin because it is now locked to the rear driveshaft. Even with one front wheel off the ground, the rear wheels cannot spin so the front driveshaft cannot either. If the front driveshaft spins then there is a problem with the TCM (likely) or internal problem with the TC (not likely). If a TCM problem is indicated, take a hammer and bang lightly on the TCM. It is on the outside of the TC and has the large wiring harness going to it. If it still won't engage, I'd replace it. You can find them fairly cheap and they are easy to replace.
That should tell you if your failure to achieve 4x4 operation is due to the TC or TCM.
Last edited by VTX1800N1; 12-28-2012 at 09:53 AM.
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The last common failure is a vacuum problem with the check valves and/or vacuum reservoir. The check valves and reservoir are in the system to maintain vacuum to the IWEs when the engine would otherwise have low or no vacuum available, such as in Wide Open Throttle or heavy load (up a hill towing/hauling) situations. The symptoms here are grinding noises heard under those conditions. A vacuum leak is causing low vacuum to one or both IWEs such that they start to engage. Since 4WD is not intended in this situation, the TC has not spun up the front driveshaft, differential, and half shafts. This means that the hubs are turning at the speed of the front wheels while the IWEs are trying to engage them and a stationary half shaft- something they were never intended to do. Thus, those wonderful grinding noises.
Remember that a disconnected/leaking vacuum hose at one IWE or diaphragm leak inside one IWE will likely cause the other side to grind. A sign of failed check valve(s) is a dip in vacuum when tested at the IWE as a friend revs the engine.
It's also possible that a grinding noise only shows up in cold weather. This can be because of water freezing in the vacuum lines (bad IWE solenoid most likely), water freezing internal to the IWE (water source again the solenoid, with water traveling down the vacuum lines) or water between the IWE and hub that prevents the spring collar from engaging the hub.
Use your vacuum tester on the check valves. On the vacuum control side, the line goes from the IWE solenoid and T's off to both IWEs. Only one control vacuum line comes out of the IWE solenoid. On the vacuum supply side, a vacuum line comes off the engine to a check valve. A check valve just means that vacuum can only flow one way- like an electrical diode. Disconnect this check valve (take it completely off the truck to test), but remember which way it went in the line (they are color-coded). If you reverse it, you will have problems. You should not be able to pull vacuum from the engine side, but it should hold vacuum going the other way. This is because the engine is the vacuum supply. When you request full throttle or place a heavy load on the engine, the throttle body opens up to admit more air, which results in vacuum in the intake plenum dropping. If your IWEs were connected directly to engine vacuum without this check valve in place (or if it malfunctioned), then this lower vacuum might allow the IWEs to start to engage when they are not intended to by the system. That's the grinding you hear when towing heavy or climbing a hill or at full throttle.
After the check valve comes a T-fitting. One end has a vacuum line that goes to another check valve and then to the IWE solenoid supply side. Vacuum flows the same way in this check valve, so the engine side should not be able to hold vacuum (when disconnected completely from the truck), but the solenoid side should. The other end of this T-fitting goes to a vacuum reservoir behind the battery. The reservoir is there to provide for a backup capacity for the system. You need to test the reservoir as well, to make sure that it can hold vacuum. If either check valve fails to hold vacuum from the solenoid side, replace it.
Last edited by VTX1800N1; 12-31-2012 at 12:56 AM.
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Remember that you can have multiple combinations of these problems. The system is a good one- the original parts just could have been better (solenoid in particular, the new one has a rain hood over it).
I should add, you may be tempted to blow any water out of the system using compressed air. It's OK to do this so long as you first disconnect both check valves and the vacuum reservoir (obviously pull the hoses off at the IWEs also). If you don't disconnect them, air pressure will destroy them. Instead of a compressor, I'd use that canned air you can get to clean dust out of computers. Just tape the straw into the vacuum lines.
Lots of people complain about this system, I think its pretty good and simple for shift on the fly. Good write up, between this one and the other on IWE with the drawing for the vacum lines you shoul be able to at least figure out what is going on within the system if not working properly. A question no one has seemed to nail down for me is the indicator position switch light and why it fails when the IWE solenoid fails, it will work in low for a while then quit completely from what i experienced and have seen other forum members post. I am going to say the signal from it to PCM or relay/swicth that it selects to 4x4 high/low doesnt pass through a particular point or through the solenoid itself.
You did address this, still doesn't tell me where or which is signaling what. I appologize as I did not read where you adresses the indicator lights, again great write up!
Follow the TSB link. It talks about water shorting out the solenoid with the result of there being no 4Hi or 4Low light on the dash when selected. Other system problems that would cause no lights are rare.
VTX...very nice write up... in your third paragraph you state that when the motor is off the IWE solenoid vents the stored vaccum...I don't think it does this...due to the fact that you need to tell the system to vent...I..E.. turn the SOTF selector to 4H...the check valves you mention keep the vacuum to the hubs. and you state that you can shift to 4L @ 3 MPH...don't think this is turn either...I have to come to a complete stop with the tranny in "N" with like you said my foot on the brake... just want to clear up my understanding of this system...once again very nice write up.
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