Drive Train Axles Bearings problem
2000 GMC Jimmy 6 cyl Four Wheel Drive Automatic 105000 miles
My Jimmy won't engage into 4wd when it's cold (about 35-37F or colder). When it's warmer, it will engage in and out of 4hi or 4lo as it was designed to do. Also, if you engage it while it's warm, park the Jimmy and then restart it the next morning while it's still cold, it will still be in 4wd and will work as expected.
I have the same vehicle with the same exact issue. I have not yet isolated the problem, but suspect it to be vacuum related or perhaps electrical contact related. I have found through experience that most mechanical malfunctions such as this are electrical/contact related. Oftentimes the issue can be corrected by tightening a loose wire or more likely re-soldering a circuit board contact that has a hairline crack in the solder.