The 4 wheel drive work on my 2005 Chevy blazer what is the most common problem with them?

The most common problem with 4-wheel drive (4WD) systems in the 2005 Chevy Blazer, particularly those using the NP246 transfer case (which is common in that year), is failure of the actuator motor. This motor controls the engagement of the 4WD system. When it fails, you'll lose the ability to shift into 4WD. Sometimes it's a simple electrical issue with the motor, other times the motor itself needs replacement.

Other common problems include:

* Transfer case problems: Beyond the actuator motor, the transfer case itself can develop leaks, wear out internal components, or experience binding.

* Front axle issues: Issues like worn CV joints, u-joints, or wheel bearings can affect 4WD functionality and often manifest as noises or vibrations when in 4WD.

* Wiring and switch problems: Problems with the 4WD selector switch or the wiring harness can prevent the system from engaging properly.

It's important to note that diagnosing 4WD issues requires a bit of mechanical knowledge or a professional mechanic. Simply trying to force engagement can cause further damage. If your 4WD isn't working, a professional diagnosis is recommended to identify the specific issue before undertaking repairs.