I'm brand new here andrecently purchased a 2002 Blazer 4dr, 4WD LS model with only 57k miles. It appears to be in very good overall condition. It has the "three button" 4wd - 2hi, 4 hi, and 4lo selections. It easily switches into 4lo (when stopped), but is very difficult (almost impossible) to engage in 4hi. Whenever I press the "4hi" button, it instead switches into 4lo. Also, it will not "shift on the fly" into 4wd high - at any speed. However, if I stop and press with the switches several times (back and forth), I can usually get it into 4hi (eventually).Once engaged, the4wd seems to work fine - doesn't make any unusual noises. Therefore I don't think it's a mechanical issue with the transfer case.

I've already checked all the obvious things - vacuum lines, connections, etc. Everything looks okay. However, I have noticed a "clicking" sound coming from the passenger side interior foot-well area when attempting to switch into 4wd high. It doesn't seem to do this with 4lo. It sounds like an electrical switch/box trying to do something - makes clicking sounds, then stops.

Also, I've read thru many of these posts, and did the "disconnect the battery" deal. This seemed to fix the problem for about 2 to three cycles, but now it's back to doing the same thing it was originally doing. In addition, I've noticed a humming sound from the right front hub after disengaging 4wd - on some occasions. However, ifI play around with the 4wd switches, and shift the trans back and forth a few times, the noise goes away completely. Therefore I suspect the hub might be partially engaged?? I'm not really sure, but think these problems are connected in some way.

Any advice or insight people could offer would be greatly appreciated. Trying to avoid a trip to the dealer. Thank you

 

Have you read the "OBD2 Non-Automatic Transfer Case Diagnostic" thread in the Tech Article (DIY) section? It will explain how to check for codes in the TCCM. If you have any stored, report back with them and we will work from there. There are a few different things that can cause this.

 

Okay, thank you, I will check out that article - and the codes

 

Okay, I ran the diagnostic test. It returned no codes - just one flash of all the lights simultaneously - which I understand means "no codes." Any further help or suggests would be greatly appreciated. Thank you

 

***Okay, quick update - found a potential very simple fix. Found the front differential was about 40 percent low on gear lube. Filled it up, now the 4x4 seems to work absolutely fine....been running it a few days now, and everything seems normal. Shifts in and out of 4x4 without any trouble. Not sure if there's a sensor involved on this, or if it's a strickly mechanical issue, but the system works normal now. Others should probably check the fluid too as a simple first step***

 

Probably a sticky mechanical issue. Glad you got it working!