Uncommanded shift into 4HI

[ComputernerdBD]

Hey everyone. Well I had something scary happen today that I didn't even think was possible. I was driving to work and toward the end of the short trip I felt the steering bind up and groan in turns. When I parked the car it was worse. I looked down and was horrified to see the transfer case lit up in 4HI mode when the switch was in 2HI when I moved it there just 10 minutes earlier. Now the 4WD has been working perfectly for the past several days and especially so on Monday morning when I drove it over 75 miles through snow in Auto 4WD. Between that and the Stabilitrak, it kept it on the road even with the ice at times. I turned the switch to auto and back to 2HI and it shifted back no problem. During my dinner break I tested it a couple times and it still feels like it locks in properly with poor turning radius on snow in 4HI and no issue in Auto/2HI. I am going to jack up the front left wheel tomorrow and check to make sure it locks properly at least. Now I have three concerns:

1. What caused it to make an uncommanded shift into 4HI while driving at 40-50mph and how to prevent it from happening again

2. If it could have gotten into 4LO, ripped the transfer case and front axle to pieces and caused an accident

3. How much damage could have been caused when it shifted. While it was only a few miles and the book says it can be moved at any speed, I am aware that is not a good idea which is why I don't move the switches on either of my trucks at anything over 1mph. I can't pull the handle on my 98 Jimmy at anything over a crawl because I have a posi-lock system. I already had $$$$ invested in a new axle disconnect assembly/TCCM on that truck in late 2007, so I don't ever want to go through that mess again.

I was looking around and found that the selector switch itself is a problem at times. I have already ordered two from Amazon (Dorman) as I am going on a trip for a week and a half (yea, bad timing) starting this weekend. I was considering calling a local dealer (against my own rules) and finding out if they have one and if it is inexpensive and keeping the Dormans as spares. Do dealers still stock these? Could it also be the TCCM? I have no Service 4WD indications or lights. Please advise. Thank you very much

 

[Mounce]

Maintenance been kept up? T-case fluid changed every 50k miles?

When you say you'd just put it back in 2hi ten minutes earlier before you noticed it in 4hi, are you sure it shifted into 2hi or could that command possibly have failed (stayed in 4hi and didn't switch) and it just reverted back to telling you what gear it was really in?

 

[kickass audio]

I am with Mounce on what happened when you shifted it out of 4 hi and into 2 hi. Also, a known issue is with the switches where they get unused and start to get dirty contacts and it messes up with the xfer case as it has no idea what real position the switch is in. I recently tore my switch apart so I could put in LED's and found that the dielectric grease they use between the knob and circuit board pads was so minimal that it was almost like bare contact on the board. I put a good amount of dielectric grease on both and all is good. Never had an issue with it but just as preventative maintenance for that.

 

[The_Roadie]

There is a double interlock (described in the Owners Manual) to protect you from inadvertent low range activation, even if the switch fails. The tranny has to be in neutral, and you have to be stopped or rolling less than 3 mph.

 

[ComputernerdBD]

Mounce/kickass audio: Interesting theory, but I could have sworn the truck was definitely in 2HI before I left... It is dry pavement now that they cleared the roads and I double checked that it completed. Plus the binding didn't take effect until toward the end of the trip. For the first part I had to make some tight turns that would not be possible in 4HI without the binding and groaning. The truck only has 35k miles on it and I changed the fluid myself last year with Autotrak fluid from the dealer. I intend on doing the same in the spring along with the front axle. So it could be a switch? Well I called the local dealer and they have one left at $30. I am going to change out the switch anyway as a precaution. The uncommanded movement hasn't happened since, but I don't want to take a chance.

The_Roadie: Perfect. So it does have some level of safety built in....

Thanks all

 

[Mounce]

WOW! 35k? Original owner?

And what year is it? (on tapatalk, can't see vehicle information)

 

[Mark20]

I've had that happen to me a while back. My conclusion was a dirty switch. Now once a month I cycle the switch back and forth a few times with engine off as well as engage AWD and 4HI while rolling to exercise the system. No problems since.

 

[ComputernerdBD]

Ok I got the switch from the dealer and swapped it out. Ended up destroying the old one in the process since I didn't pull the dashboard. The metal clips broke off and fell behind the dash... The new switch works well and I moved it through all positions without issue. It seems the 4HI setting works fine still. I tried it on some ice and made turns and I get the normal bind and it gets good traction.

The contacts look clean on the old switch but the grease layer is thin.... I am confused. Just looking at this switch, how can it go into 4HI on it's own unless there was a short circuit somewhere? Thanks