4wd working or not?
 

Just bought a 08 suburban Ltz w 50k miles.

I got stuck in some pretty wet grass. I had it in 2 wheel drive so I switch it into four-wheel-drive. I put the transmission in neutral before I shifted into four hi. The light was blinking on for high and then turn to solid. I put the transmission back into first gear and then step on the gas but only the rear tires spun I couldn't believe it I was stuck in a flat wet grassy area. I tried shifting into four low using the same process but no matter what I did I could not get in the front tires to engage. I could even hear the tc engaging and disengaging when going in and out if 4wd. I did turn off the trac control when I was in 4 hi but made no diff

I assume the front tire should be spinning right? Felt like a lamo

Aaron

I also had my wife roll slowly while I was lying on the ground watching the front driveline. It turns in 4wd and doesn't in 2wd which is what I would expect. Adds to the confusion for me of why the front wheels don't spin in 4wd.

Jan Rosenberg
 

When you engage 4 WD the front axles have to be engaged which should happen automatically. Sound like a problem with the front axle / diff. Actuator system.

I have a bad feeling you're right. Some how power is not being transferred :(
Wish it was more old school mechanical. Hope it's not turning my good deal into a bad one lol.

Thanks for your thoughts. Anyone else?

Aaron

It is not necessarily an expensive or terribly complicated problem. I checked All Data, and there is a little confusion on T.C identification. They refer to a BW 4485-NR3 and a MP 3023/3024-NQH. I believe you have the latter because the first one is a single speed. In diagnostics they refer to NP8, and that does have a front differential actuator. I think that is what you need to diagnose.Be very careful. If you cand put it in 4WD then get the tires of the ground, see if the front driveshaft is turning and the front wheels are not.

You're right Aaron, anytime you shift out of 2WD, both front wheels should be turning. Hard to say exactly what it is, but, you might put it up on a chassis rack, engage the 4WD, and see if you see any shafts turning. That should help localize the problem.

issue
 

You don't need Neutral to engage 4 high.

and I agree, it sounds like an issue with the front diff/hubs engaging.

Here Are the results of my testing with all wheels off the ground

In 2wd /first gear
- rear wheels turning
- front driveshaft turning
- front wheels not turning
In 4wd hi /first gear
- rear wheels turning
- front driveshaft turning
- front wheels turning
- I can stop both front wheels at the same time with a friend. This doesn't seem right. I should only be able to stop one right?

I can hear the encoder/actuator motor engaging and I hear a clunking noise going into 4wd. Could the motor still be bad?

Front axles
 

If you can stop the front wheels but the front driveshaft still turns then it is definately a problem with the front axle / diff. Actuator system

Its your hubs, they need to be cleaned properly and you can do it.