My 4x4 1999 gmc jimmy slt has a problem, when i pust the auto 4x4 4hi or 4lo button i hear the axles lock but the light next to all the buttons no matter which one i push always keeps blinking and never solidifies, after a few minutes the axles unlock and go back to 2hi, i never have a problem getting into 2hi at all just everything else, basically i cannot get out of 2hi. is there an adjustment i can do or something to get them to engage fully??

THE TRANSFER CASE MOTOR IS ONLY FOR 4WD LOW. That would have never been the problem as soon as you confirmed it shifted into 4wd Low. 2wd and 4 Hi work off of vacuum. You may have one or two issues. A vacuum leak up by the front axle that engages the 4wd HI or the sensors on the transfer case.

change your push button switch had same problem

• Shifting from 2HI to 4HI Press and release the 4HI button. This can be done at any speed, and the front axle will lock automatically.

• Shifting from 4HI to 2HI Press and release the 2HI button. This can be done at any speed, and the front axle will unlock automatically.

• To shift from 2HI or 4HI to 4LO, the vehicle must be stopped or moving less than 3 mph with the transmission in NEUTRAL

• Hope this helps.

my jimmy also did this i disconnected positive battery terminal for about 20 seconds and this fixed mine.

To shift into 4lo you must come to a complete stop, put the transmission in neutral, and step on the brake pedal, then push the 4lo button. To shift out of 4lo, do the same thing. If it's not going into 4hi, check every vacuum line you can find. Everything is vacuum operated. If your vacuum lines are old and crusty or mushy, they may collapse when vacuum is applied. There is one vacuum hose that is hidden under the battery tray that almost always comes loose, and it is the one that locks the front axle. You will need to remove the battery and tray to get to it. If the hose is dried out or stiff, replace it with a new one that is flexible enough to make the sharp bend required to hook up to the actuator. Also check the actuators under the vehicle at the transfer case and front axle.

In addition to transfer case engagement via an actuator on the "T" case there is a front axle actuator. On my Blazer which I'd bet is very similar.. There was a vacuum diaphragm under the battery which operated a cable to "lock in" front axle. make sure you have vacuum supply when asking for 4 wheel operation and make sure cable is not seized. If this checks out o.k. back to transfer case. your question asked about front wheels locking so I assumed your "T"case was working

You should be able to put in 4x4 while in drive less than 35mph. Mine had a switch to turn to engage or dis-engage.

If they are blinking I believe it means that there are fault codes present in the pcm. You need to get the computer scaned to see if there are an codes present. If you live near an Autozone or Checker autoparts they can scan it for free.

vacuum leak or vacuum locker solenoid problem. a great way to check for both is to remove both vacuum lines from the solenoid (located on firewall above destributor), and put a connector between them, push the button on the dash and see if it locks in.

You need to see if the transfer case engagement motor is defective.