i had the same message and replaced the switch because of a loud clunk and jumped when i put it into 4wd idk if yours does that but i replaced the 4wd servo motor that selects 4hi or 4lo and that seemed to fix all my problems. hope that helps

 

got a quick question dont wanna start a new thread on, mine goes into 4hi great but never locks into 4lo (is it the T-case servo?) just keeps blinking like its trying to shift into 4lo but never does. and ive never had the service 4wd light come on.

 

got a quick question dont wanna start a new thread on, mine goes into 4hi great but never locks into 4lo (is it the T-case servo?) just keeps blinking like its trying to shift into 4lo but never does. and ive never had the service 4wd light come on.

do you put it in neutral when you try it

 

i had the same message and replaced the switch because of a loud clunk and jumped when i put it into 4wd idk if yours does that but i replaced the 4wd servo motor that selects 4hi or 4lo and that seemed to fix all my problems. hope that helps

How much was the servo and is it easly to do?

 

How much was the servo and is it easly to do?

i think it was like $300 it could have been more but there is a core charge too. and it wasnt really that hard the main thing was ya have to take the front driveline off to get to it but once thats off its way easy.

 

do you put it in neutral when you try it

damn I feel like an idiot! never knew I had to have my truck in neutral becuse my dad's and friends trucks (both chevys) dont have to be in netural.

 

It was the servo motor and I also saw the wiring harness into it was rubbing the driveshaft and wore the insulation off the wires. $800 for the new wire harnes, servo motor and labor

 

Ouch. I was going to guess that it was the encoder motor sensor. it seems to be a common problem with these trucks. mine went out at 115k. my buddy's just went out in his 06 at 160k.

 

Jumping in the end of this....

Had the service 4wd message popping up for the last three weeks, it would go off for a couple days, then pop back up, then go off, etc. One of those, I'll get to it later because the truck seems to be running ok otherwise things.

Well today, I start hearing a grinding and the message pops up again. Sounds like when you're in 4wd on dry pavement and trying to turn. Freaked me out because I was in the middle of a 30 minute commute. I made it, and have done a little research and seems like this actuator motor might be the culprit. Truck has 116,000 miles on it (just about the same as Matt's had).

Is this the correct looking part?
Can anyone point me in the right direction as to a step by step to replace it? I don't think I even want to know how much the dealer would charge!

Thanks guys. Oh, and life knows just when to kick you in the nuts. My wife and I will be closing on our first house and will be shelling out the down-payment next week. DOH!

 

Jumping in the end of this....

Had the service 4wd message popping up for the last three weeks, it would go off for a couple days, then pop back up, then go off, etc. One of those, I'll get to it later because the truck seems to be running ok otherwise things.

Well today, I start hearing a grinding and the message pops up again. Sounds like when you're in 4wd on dry pavement and trying to turn. Freaked me out because I was in the middle of a 30 minute commute. I made it, and have done a little research and seems like this actuator motor might be the culprit. Truck has 116,000 miles on it (just about the same as Matt's had).

Is this the correct looking part?
Can anyone point me in the right direction as to a step by step to replace it? I don't think I even want to know how much the dealer would charge!

Thanks guys. Oh, and life knows just when to kick you in the nuts. My wife and I will be closing on our first house and will be shelling out the down-payment next week. DOH!

Here's a replacement for the encoder motor. I'm betting that you could've gotten away with replacing the sensor at first. That sensor made my truck think that it was in 4lo when I was doing 65mph down the interstate, but luckily, it never actually shifted into 4lo.

Removal
1. Shift the transfer case into Neutral.
a. Chock the tires (I chocked in front of the fronts and behind the rears, so it couldn’t roll either way.)
b. Set the parking brake.
c. Turn the ignition to RUN.
d. Shift the transmission into Neutral.
e. Push and hold the 2HI and 4LO buttons for ten (10) seconds. (The red Neutral light should come on.)
f. Shift the transmission into Reverse for one (1) second, then into Drive for one (1) second.
g. Turn the ignition to LOCK.
h. Shift the transmission into Park.

2. Remove four (4) 15mm bolts from the transfer case skid plate.


3. Loosen the hose clamp on the transfer case side of the rubber boot. Pry the clamp loose, moving it forward towards the front of the truck.


4. Mark the relationship of the front drive shaft to the front axle using the Sharpie.


5. Remove four (4) 7/16” cap bolts.

6. Knock the front U joint loose.

7. Slide the front drive shaft towards the rear of the truck, swing the front of the front drive shaft down, then slide the entire front drive shaft forward and remove.


8. Remove three (3) 15mm bolts from the encoder motor.


9. Unplug the electrical connector. The connector is attached to the truck using one of those little plastic clips that breaks when you try to remove them. Pinch the sides of the clip together using needle nose pliers or your fingers, if you have hands, not huge bear paws.


10. Remove the encoder motor.

11. Inspect the black gasket. If it’s damaged, replace.


12. Transfer the gasket from the old encoder motor to the new encoder motor.


Reinstallation
13. Reconnect the electrical connector.

14. Reinstall the encoder motor.

15. Put Loc-tite on the three (3) 15mm bolts that connect the encoder motor to the transfer case.

16. Reinstall the three (3) 15mm bolts into the encoder motor.

17. Shift the transfer case into 2HI.

18. Slide the front drive shaft into the transfer case.

19. Line up the marks on the front drive shaft and the front axle.

20. Reinstall the four (4) 7/16” cap bolts and straps onto the front U joint.

21. Retighten the rubber boot’s hose clamp onto the transfer case.

22. Reinstall the skid plate with the four (4) 15mm bolts.

 

Thanks Matt! :shake:

I checked the TREC fuse under the hood and that's still good. Drove it home the 30 minutes last night and didn't have any warnings come on or grinding sounds. All my lights still work on the switch and I even got brave enough to put it into 4hi on a straight road for .5 mile. It switched right in and then when I went back to 2hi it switched right out. It seems like the switch is functioning well.

Got up this morning and 1 mile into my drive, the service 4wd message comes back on. Drove for about 15 miles, pulled into a gas station, shut the truck off, waited a minute, started it back up, and within 1 more mile the message came back on. I didn't hear/feel any grinding this time though.


I haven't gotten to buying parts yet. I need to soak everything down for a couple days with some PBblaster. Living in the salt belt of Michigan has every single bolt on my truck seized up. Once I slowed down and could think clearly, I do remember that sensor going out when I first bought my truck in 2007. It was replaced under warranty then.

I looked into changing that small round sensor, but as much as it sucks, I need a simple fast replacement as almost all my tools are packed up for the move into the new house. I know it doesn't take a lot of work, but I don't have time to mess around with taking that motor apart. besides, me and electronic parts don't get along real well. Near as a quick part number check confirms, it's like $100 to change the sensor...and $200 to change the whole unit. I think I'll go that route.

One other thing that I want to do is to clean up the ground contact on the frame. Does anyone know where that ground is located? I crawled around for 5 minutes and I found two grounds on the outside of the frame, almost directly below the front of my driver door. Are one of those the motor ground?

Thanks again guys. The GMFS family is the best!