4 wheel drive will not engage - 1988 Chevrolet C1500

There are a few potential issues that could be causing your 2004 GMC Envoy SLT to go into 4-low but not 4-high or 2-wheel drive. Some possible causes include:

1. Transfer case issues: The transfer case is responsible for controlling the engagement of the different drive modes. If the transfer case is damaged or malfunctioning, it may not be able to engage 4-high or 2-wheel drive.
2. Shift motor issues: The shift motor is responsible for controlling the engagement of the transfer case. If the shift motor is damaged or malfunctioning, it may not be able to engage 4-high or 2-wheel drive.
3. Vacuum issues: The vacuum system is responsible for controlling the engagement of the transfer case. If there is a problem with the vacuum system, it may not be able to engage 4-high or 2-wheel drive.
4. Wiring issues: The wiring that controls the transfer case and shift motor can become damaged or corroded over time. This can cause the transfer case to not engage 4-high or 2-wheel drive.
5. Control module issues: The control module that controls the transfer case and shift motor can fail. This can cause the transfer case to not engage 4-high or 2-wheel drive.

It's best to diagnose the issue by a professional mechanic, who can perform a proper diagnosis and repair the issue. They will be able to determine the specific cause of the problem and recommend the appropriate repairs.

Check 4 w actuator.

this is a rear wheel drive vehicle and as such the rear wheels are always engaged.when in 4 wheel drive the transfer case in gages and the front differential connects and is engaged.unless the 4 wheel drive is engaged the transfer case just free wheels.

If I read this correctly ( which I might not have, bit early for me ), the front drive shaft will engage ( from the transfer case ) but the front wheels are not engaged ?

If so, sounds like either the vacuum from the IWE ( Integrated Wheel End ) is not being released, or the IWEs have had an issue with part vacuum ( damage vacuum lines ) and the IWE gear is rounded off.

If you pull the vacuum lines at the IWEs ( there are 2 lines, 1 is the vacuum line, the other is the vent tube that routes up into the engine compartment and is not attached to anything ), the front wheel should engage ( might need a 5 * turn to mesh the gears ). With the vacuum lines off, jack up the front axle ( take precautions, chock the rear wheels, parking brake, jack stands, etc ) see if the front wheels are engaged ( turning one wheel should turn the other ). The option is to do this after the truck has sat over night, and the vacuum has been released out of the vacuum reservoir.

If the wheels turn correctly ( engaged ) I would think the contact plates in the transfer case are not making contact. Good starting point for this is the connector on the side of the transfer case, some times this gets gummed up, and the pins do not make good contact. The contact plates in the transfer case are used for a few things, one of them is to signal the IWE solenoids to release vacuum to the IWEs.

Operationally vacuum holds the IWE ( Integrated Wheel Ends ) out, and once vacuum is removed the spring engages the IWE.

Here is a black diagram of the IWE vacuum system

The internal lockouts are not engaging so they need to be replaced

There is a vacuum switch on the transfer case left side,up high!(Most have 2-3 vacuum hoses) That switch is bad!

there are vacum line one on each side behide the wheels see if they are broke or leaking i had the same problem

Check the fuse for the four wheel drive before taking another step,it is electrically engage,hope that help you and clear your mind

It depends, look at the hubs on your front wheels? Is there a knob in the center of the wheels? If so, then turn this knob to the right and you will have engaged the 4 wheel drive? If you do this, however, make sure you engage the 4 wheel drive inside the truck (if your truck has a 4 wheel drive gear shifter).
Oh other Rangers you have a knob on the inside of the cab it should be somewhere on the dash. You can turn it to the right and this will engage the 4 wheel drive.
Finally, when you engage the 4WD make sure the engine is cut off so it doesn't mess up your transfer case.

Having 4 wheel drive is not actually the case unless you have limited slip on both axles. Do you know if one wheel will spin on both axles. If you can't get either wheel to spin on the front axle and one will spin on the rear then I would agree your not getting front wheel drive. Since you can tell a difference between hi/lo the transfer case is definitely engaging