Hey guys n gals,
Read a bunch of threads on this and haven't seen one like the issue I'm having. When it's cold, say, below 40º, the transfer case acts up. My driveway is super-steep and super-short, so when I pull in I always put it in 4 LO for the eventual back-out next time.

After backing out and pulling forward a little, I stop, put it in neutral, and select 4 HI LOCK. Transfer case goes clunk, light goes out in the 4 LO button, but the transfer never completes. 4 HI LOCK flashes and the 'Service 4wd' message comes on. Now I don't know where the drivers are, 4 HI LOCK or just 4 HI.

We've been getting alot of snow and this Ole Miss boy don't cotton to such. With 4 LO inop I'm pretty nervous about getting stuck. After the truck is thoroughly warm, like when I get to town (30 minutes) and shut it off for a few, when I start it back up all is well. It's a colder-than-a-witch's-knickers issue.

So is the motor just not disengaging a tiny bit at the end of the cycle, enough to make the system go into BS mode and shut down? You think pulling it and cleaning it up will do the trick, or just get a new/reman unit from GM? Or y'all think it might be something else?

On a side note: is 4 HI like all other 4wd vehicles, actually just 2wd with the fronts free-wheeling? If not, what's the diff between 4 HI and 4 HI LOCK?

Thanks y'all. Merry Christmas! I'm working

 

The H2 is in all wheel drive mode at all times, there is no freewheeling of the front axle.

The difference between 4HI and 4HI LOCK:
In 4HI you get a 40/60 percent front-to-rear torque split at the axles.
In 4HI LOCK you get a 50/50 percent front-to-rear torque split at the axles.
In 4LO you get a 50/50 percent front-to-rear torque split at the axles at a 2.64:1 gear reduction.

Examples of when to use each mode:
4HI - for normal, everyday driving on mainly dry road surfaces at any speeds.
4HI LOCK - for semi-slippery surfaces like snow, light sand or wet areas. DO NOT use 4HI LOCK on dry or solid pavement !!!!
4LO - for severe OFF-pavement use, such as crawling over large rocks or logs.

4HI LOCK or 4LO should ONLY be shifted into when NEEDED.

So there really is no reason for you to be using 4LO to just get in or out of your driveway. In fact I would say it's a bad idea.


As for your shifting problem, next time when shifting to 4HI from 4LO try backing up a few feet after the shift. Sometimes things get stuck slightly in the transfer case.

 

Without being in 4LO the wheels spin, even when it's dry. The driveway is that steep. No way I'd try it in the snow and ice without 4LO. I've had two other folks visit with 4wd vehicles who had to lock their hubs to get out so don't think I've got a choice, other than use a helicopter to get in and out of here.

I pull forward, sometimes several hundred feet, before pushing the 4HI buttons but will try backing instead.

 

Backup AFTER shifting into 4HI

 

Yup, said I would try that. Thanks for the reply.

 

Tried backing up before going to 4 HI, same result. System only thinks about it for 3 seconds before giving up and saying to service the 4wd. Again, system recovered after the 30 minute drive to town, shutting the truck off while I got our mail at the post office, then restarting.

On the road now till the 30th. When I get back I have two weeks off so I'll make room in the garage and pull the shift motor, see what it looks like. Bound to be some corrosion on the electrical connectors, too.

 

Changed the transfer case actuator and encoder motor and everything has worked fine, even down to 15º. Been about two weeks now, shifts every time. There was no grease on the input shaft so lubed that up, also put electrical grease in the connector to keep moisture out. So hopefully this one is solved.

 

How long did it take you to swap out the actuator? Did you have access to a lift or did you simply climb under the truck?
Was it a difficult job?

Thanks.

 

Easy-peasy. No lift needed, plenty of room under there. Three mount bolts, plus one for the bracket holding the plug. Takes longest to figure out how to unplug the harness. I think GM techs must have a two-week school just for that. Will be a 10 minute job if you get it figured out quickly. Think there's a plastic retention tab that has to be pulled out first so you can then push on the release tab and pull the plug apart. Good luck.

 

Thanks Flyday58. Great information. I will tackle this job on my own!

Will try to remember to take pictures and post!