If you own a Ford F150 and wondering why the 4WD won’t engage properly when you select 4H, this article is for you. We’ll also cover what causes the grinding noise while driving, and what 4WD components might need replacement on your F150 4WD system.
Why won’t my F150 4WD not engage? The 4WD system of your Ford F150 can fail to engage due to any of the following reasons:
- Failed 4WD Actuator
- Damaged Vacuum hoses
- Failed Vacuum Solenoid
- Transfer case shift motor
This article will also cover how you can troubleshoot and diagnose the 4WD problem without any tools, as well as other common 4WD problems found on the F150 Ford Pickup.
So let’s dig into what could have gone wrong and look at the obvious culprits.
Ford F150 4 Wheel Drive Not Engaging
The nice thing about diagnosing the F150 is that you won’t need any high-tech equipment and specialized tools to diagnose the problem. You just need to understand how the 4WD system works and where to look.
So what’s the first component we need to find?
Your first point of trouble-shooting should be to locate the vacuum system.
F150 Vacuum System Diagnosis
The purpose of this test is to make sure you have vacuum pressure and the hoses are void of any leaks and cracks.
The first thing you want to do is locate the solenoid. It is usually situated on the passenger side of the truck next to the battery. What you want to accomplish is, test the vacuum line for pressure. You won’t even need a vacuum gauge to accomplish this or any fancy testing equipment.
So to test for vacuum, you need to remove the vacuum hoses from the solenoid which is located against the firewall. There are 2x vacuum hoses held together with a black plastic housing. The one line (check valve) should have a constant vacuum when the engine is running. The second hose should only have vacuum pressure once 4WD is engaged.
To test for vacuum, you remove the hose from the check-valve connection and stick it in the second hose that feeds pressure to the IWE’s. That would provide a permanent vacuum when the engine is switched on and sucks the diaphragm from the IWE back in, allowing the front wheels to rotate freely.
To test, jack the front of the truck up and test if both front wheels are free spinning.
Vacuum Hose Troubleshooting:
Transfer shift motor
The transfer case shift motor was quite troublesome and problematic in earlier models of the F150 life. Since 2004+ they’ve been more robust and seldom cause issues.
To test if the actuator is meshing and engaging, remove both lines and with the front still raised, the front CV shafts should be engaged and be rotating as well.
When there is a vacuum in the lines the hubs will disengage and the truck will be in 2WD and once the vacuum pressure is activated the 4WD will be engaged once the hub and actuator spline are engaged.
Ford F150 IWE Solenoid Trouble-shooting
Before you run any tests make sure the bottom vacuum lines are connected back up. DO NOT connect the top vacuum lines. Next, start up the truck in 2WD and test for vacuum pressure from the top pipe. There should be vacuum pressure. Next, with the car in Park, engage 4WD and test for vacuum. There should be no vacuum on the top pipe. That will determine if the solenoid is actually working without any fancy electrical equipment.
In many cases, moisture is the cause of the solenoid failing. Older style solenoids had no cover/hood to prevent moisture from getting in. Replace the new design with the hood to prevent moisture damage from reoccurring.
So, to further diagnose, remember when the truck is in 2WD mode there should be a vacuum on the bigger hose down below. The front driveshaft should not rotate when you turn the tire. Only once 4WD is engaged, should the CV and front drive-shafts rotate. If there is a strong vacuum and the driveshafts are still rotating, there is possibly a problem on the wheel end with the actuator that engages the hub. This will require you to remove the front wheels and investigate a bit further.
2007 F150 4 Wheel Drive Problem (Not Engaging)
If you drive an F150 from 04 upwards with the vacuum solenoid, and you’re experiencing problems with your 4WD system, then this section is for you. The solenoid is usually situated on the passenger side of the engine bay behind the battery, mounted against the firewall.
A problematic or faulty 4WD system on the F150 will display any of the following symptoms:
- Metal on metal grinding while driving
- Front axle jerking
- Loud metal noises coming from the front axle.
How Do I Fix My Ford F150 4 Wheel Drive?
When the truck is in 2WD mode, which it should be when driving on a high traction surface like pavement or highway roads, the vacuum is active and disengages the front hubs by means of the front actuators sucking. Once the vacuum is lost and the actuator cannot disengage the front hubs, they will lose pressure and automatically engage, shredding the hub gear.
This is when you will experience the grinding and metal on metal jerking effect since there is no more vacuum on the lines to disable 2WD mode on the front hubs.
So possible culprits could be:
- Front actuator failure
- Leak on the front vacuum hose
- Front hub failed
- Front Hub seal blown
- Failed Solenoid
The wheel will need to be removed and stripped to inspect what the actual problem is. If any moisture got into the solenoid and managed to cause damage, that will need replacement too.
Ford F150 IWE problem
There seem to be quite a few problems with the IWE system on the F150 4WD trucks. The problem results in intermittent grinding from one or both of the front wheels while driving. Loud metal on metal and shuddering sensations are also reported.
So basically this means there has been a loss or drop in vacuum pressure somewhere in the 4WD vacuum system. This can be caused by any of the following:
- Faulty IWE
- Crack/leak in the vacuum line
- Perished rubber seal inside hub
- Faulty actuator
- Bad Solenoid
Now the grinding noise you are hearing is when the vacuum system losses pressure and the hub is engaging while you are driving causing the metal hub and spline to grind. Under light acceleration, the check-valve doesn’t close and hereby pressurizes the system causing the hubs to partially engage or attempt to engage. This causes vibration and rock in the rotor. Often times the sensation can be felt through the steering.
Watch the following video:
How to Test IWE Solenoid
You can test the IWE by jacking the front of your vehicle up while the engine is running. Make sure the drivetrain is in 2WD mode first. While the engine idles/runs go to both front wheels and rotate them. The front driveshaft should NOT turn with the wheel since the vacuum line is pressurized, thus keeping the hubs open and the truck in 2WD by sending all the power to the rear axle.
Next, engage the 4H and repeat the test. The driveshafts should now move with the wheel. Test both front wheels again. If one or both are not moving and engaged with the transfer case you shouldn’t be able to turn the wheel. If the wheel rotates with the driveshaft and the truck is in 4H you have a problem with the IWE on that wheel.
Ford F150 Grinding Noise When Accelerating In 4wd
If you are experiencing a problem with a grinding noise coming from the front of your vehicle while accelerating then this section is for you. The problem can occur without any prior warning signs. Fortunately, it’s a cheap and easy problem to diagnose and repair. The problem happens randomly and for longer periods each time. If you let off the gas or accelerate, it won’t make much of a difference with regard to the grinding noise.
In the case of the automatic transmission, the truck might refuse to shift up to a higher gear and will require you to manually shift up.
The problem again is more than likely the IWE. There is a service bulletin regarding the replacement of a faulty IWE Service Bulletin which you can read here:
Basically, The IWE requires constant vacuum pressure to keep the drivetrain in 2wd mode. Once there is a leak the pressure is lost and the hub will “dislocate” and attempt to engage 4H. If there is a leak or only partial vacuum pressure loss, the Hub won’t fully engage. If the IWE fails completely the 4WD system defaults to 4H even with the interior selector set on 2H. The audible grinding noise is the metal hub trying to engage the front driveshaft, hence the metallic grating noise.
I must say for such a high-tech well-packaged truck, the 4WD system is still rather basic. Fortunately, it’s a relatively easy problem to troubleshoot. You can definitely carry the small replacement parts with you on an extended Overlanding expedition. I guess that’s what they were going for, simplicity and can be repaired with very basic tools. A sign of a good reliable off-road truck.