My1992 gmc sierra4x4pickup will not shift into 4wheel drive HELP!!!!

Most 4x4 systems require the trans to be in neutral to shift into or out of 4x4low.

Depends on the year of the truck. If it's old then it sounds like a damaged transfer case. If it's newer it may be a sensor.

You shouldn't have to use 4wd to tow a boat out of the water. Does your truck have a 2wd button or just the 4high and 4low button? If you have a 2wd button, put tranny in neutral and then hit the 2wd button. If you just have the 4high and 4low button, put the tranny into neutral then press the 4high button twice (Once to get back into 4high, then again to get out of 4high and back to 2wd).

It's very common for the front differential actuator to fail on these.

NO THERE SHOULD NOT BE ANY NOISE WHEN ENGAGING OR DISENGAGING 4LOW OR 4HIGH

does it have auto hubs, if so check the vacuum switch at tranny side

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Good Evening. 4high is a simple deal to get working. 4low has a few more steps. First of course is starting the truck, shifting down into neutral at a stop then put it in 4low. After doing so then put it down in drive 4low should now be engaged. And to take it back out of 4low simply reverse the operation. Any other questions let me know, becuase if it can do 4high the shifting motor can do 4low.

If you're going too fast, the 4low will not work, if you push 4high, it should do good for you. The 4lo is for creeping, and torque. The 4high works almost as good as AWD. Usually up to about 45-50mph. Hope that helps

If it is the push button shift you need to have the transmission in neutral with the truck running.I think the manual shift ones are like that as well.
Hope this helps........Good luck!

transmission has to be in nuetral to go back out of 4low