Truck refuses to go into four-wheel drive

My truck will not go into four-wheel drive. No SES or other lights are on the dash.
Experienced mechanics share their insights in answering this question :
There is usually a certain procedure that is necessary for the switch to four wheel drive, such as selecting the neutral option on the transmission, or being stopped. If you have tried these and the vehicle still will not switch, there could be some electrical fault blocking the action. There may be a code stored, or lack of data from a sensor, that is disabling the four-wheel drive. Have a trained mechanic, such as one here at YourMechanic, come to you and diagnose any potential electrical issues.

How to Identify and Fix Common car Problems ?

Our sources include academic articles, blog posts, and personal essays from experienced mechanics :

The 4WD transfer case encoder motor position sensor or the selector switch may fail causing the service 4WD message to be displayed. Fault code(s) stored in the transfer case control module will be of assistance in determining the exact fault causing the message to be displayed.
The “Service 4WD System” message does not mean routine maintenance of the 4WD system is required. The “Service 4WD System” message indicates a problem with the 4WD system that should be properly diagnosed and repaired.
To reset the Change Oil light turn the ignition on but do not start and then push the gas pedal 3 times. The Service 4WD light is most likely the 4WD switch on the dashboard. If the lights are acting funny then the switch needs to be replaced.
Faulty Switch – If the switch itself is bad, it won`t let current flow from the battery to the solenoid, and won`t allow the transfer case to engage four-wheel-drive. Even if the switch feels fine, it could be corroded, dirty, or broken internally.
If you believe you have shifted into gear properly but the light is still on, get to a professional mechanic as soon as possible, as this may indicate a transmission issue.
4WD Malfunction Service Required. The four wheel drive system is not operating properly and the powertrain fault indicator illuminates. See Warning Lamps and Indicators. If the warning stays illuminated or continues to illuminate, contact an authorized dealer as soon as possible.
Have someone stand outside of the car and watch the tires. As you drive into the tree, your tires will try to get traction. If all four wheels of your car are moving, your four-wheel drive is doing its job!
The 4WD system is engaged or disengaged by rotating the control for both front wheel hub locks from the FREE or LOCK position, then manually engaging or disengaging the transfer case with the floor-mounted shifter. For increased fuel economy in 2WD, rotate both hub locks to the FREE position.
Our four-wheel-drive service, performed by our ASE-Certified Technicians, includes inspecting the transfer case, locking hubs, final drive, drive axles, and both front and rear differentials for leaks and wear. We also drain and refill all fluids according to your manufacturer`s recommendations.
In some cases, no more than 30-36,000 miles. And in some cases it may be as frequently as every 15,000 miles. Also look for any kinds of leaks when you`re under it.
Our four-wheel-drive service, performed by our ASE-Certified Technicians, includes inspecting the transfer case, locking hubs, final drive, drive axles, and both front and rear differentials for leaks and wear. We also drain and refill all fluids according to your manufacturer`s recommendations.
4WD Malfunction Service Required. The four wheel drive system is not operating properly and the powertrain fault indicator illuminates. See Warning Lamps and Indicators. If the warning stays illuminated or continues to illuminate, contact an authorized dealer as soon as possible.

Relevant Questions and Answers :

the most relevant questions and answers related to your specific issue

Started Three days a go. When I drive the car it doesn’t go in to gears but shows AT.
ANSWER : This kind of reaction is often a sign of low transmission fluid or a faulty transmission control solenoid. As you know, automatic transmissions use pressurized hydraulic fluid to change gears. Every time a gear change is required, the car’s computer activates a transmission solenoid, which directs transmission fluid into the valve body to engage the correct gear. When this is faulty or not working properly, this can cause a delay in gear shifting or in some cases cause the car to not shift at all. This type of problem is amplified any time the transmission is low on fluid creating a drop in hydraulic pressure. I would recommend having a professional from YourMechanic come to your location to diagnose and inspect your vehicle.

What can cause the RPMs to go super high while driving at one constant speed?
ANSWER : Hi There,
It sounds like you are describing the symptoms of a failing throttle position sensor. The throttle position sensor monitors the throttle position of the throttle plate inside the throttle body in relation to your foot position on the gas pedal. Based upon the inputs from the sensor reading your foot’s position on the pedal, the ECU then makes the direction to supply more or less fuel to the motor. When this sensor is not working properly, this can cause intermittent responses when pressing the gas pedal. I would suggest having a professional from Your Mechanic come to you home to diagnose and inspect your vehicle.

My car want go drive but will go in reverse and shift in 1 or2 and drive some, so what could it be.
ANSWER : This is an internal transmission problem with the valve body or the 1-2 sprag unit binding internally in the transmission. Have a qualified transmission diagnose the problem firsthand to pinpoint what is going on. The mechanic may have to do a pressure test to isolate the cause of the shift concern.

Every morning or when I use my truck i put it on drive I press on the gas and the engine will rev up but the truck goes very slow
ANSWER : Hello. I have a couple of ideas. You mentioned it happens in the morning and this indicates the truck is cold. When the seals in a transmission get old and hard, they allow ATF to leak internally and the transmission cannot build enough pressure to move your car forward. Once the car warms, the seals soften and seal. This will affect every gear, including reverse.

I assume, when you say the motor revs, you have a tachometer and the RPM’s rise but the car does not match speed. If this is the case, then the above explanation still applies. If you don’t have a tachometer, but the motor just makes a loud noise as if it were revving high, this is most likely the fan clutch pulling more air through the radiator. This will make a very loud rushing sound that sounds very much like the motor is revving high. It may be that the motor is not running well when cold and lacks power.

Either way, you should have one of our qualified technicians check it out. They can come to your car’s location to test the vehicle and diagnose the loss of power symptoms.

I had my truck towed on a flat bed tow truck and now it is vibrating really bad and it sounds like my tires are howling
ANSWER : The problem sounds like you have flat spots on the tires in the rear when the tow truck operator dragged and pushed the truck with the transmission locked. I would recommend having a vehicle safety inspection to see if there is tire damage or other possible damage done by the tow truck. Have a mechanic from YourMechanic come and do the inspection and check the problems for you.

Hi, I have a 2003 Ford Taurus. Going down the HWY it stopped having the driving power to go. Engine is running. Pulled o er and a
ANSWER : It sounds as if you are having further issues with your transmission. If the vehicle will only go forward and not reverse, it is possible that a shift solenoid replacement will resolve the issue. It is also possible that internal transmission damage may have occured. I would strongly recommend having your transmission inspected by a qualified professionial who is proficcient at transmission diagnosis. When your vehicle is hesitating to move forward, this sounds like the transmission is slipping. Maintaining proper fluid levels is essential to proper transmission operation. Be sure to have the transmission checked for leaks as well during this inspection.

My truck won’t allow me to change gears even when pressing the clutch. No gears go in at all. Makes it impossible to drive.
ANSWER : Hello, this concern is possibly the slave or clutch master cylinder failure. These two components use brake fluid to apply pressure for movement of the clutch system. This fluid breaks down in time and causes the seals to fail (leak). A low fluid level would cause this concern as well as internal leakage. Replacement of components would be necessary. This type of concern would need to be inspected. If you’d like, a certified technician from YourMechanic can come to your location to diagnose your vehicle, and possibly replace your clutch master cylinder if need be.

When driving and going over 55 mph the car starts shaking like it is going to cut off.
ANSWER : Hi there! There are several reasons why your TL can act this way.

First off, if this behavior is predominantly after the car has been sitting overnight or longer, it can be the result of "flat-spotting" – the low profile tires, with very stiff sidewall, develop "flat spots" where the tire sits on the pavement. This is overcome with 5-10 miles of highway driving, and the tire heat up a bit, and air pressure in the tire makes them round again.

The second possibility is out-of-balance tire/wheel combinations. Your tire shop can check the balance for you, and correct balance if necessary.

The third possibility is an axle with bad CV joints. If the CV joints are worn, they essentially "wobble", and this vibration is transmitted into the structure of the vehicle – which you could feel both with the steering wheel, and "seat-of-the-pants".

To avoid any unnecessary repairs, I would recommend having the shaking symptom diagnosed by a mobile, professional mechanic, such as one from YourMechanic, to diagnose this problem, get an accurate assessment of damage and cost estimate for repairs.