Help! My 4WD Doesn't Work :(

Hey TT'ers,

Quick Question

My 4 wheel drive just died on my 2001 Chevy Suburban.

This is basically my wife's kid hauler and it's not really been offroad much (except for that time when I drank a 5th of Wild Turkey on the camping trip!)



[Just kidding. That is NOT my Suburban] :applause:

Anyway, we had a big snow storm here in Bend, Oregon for 2 weeks and the rig was in 4WD the whole time.

All the sudden it WILL NOT go into 4WD. The front wheels are NOT getting power.

It's either an electrical problem or mechanical program for sure, but what should I look for?

I gotta get this thing fixed before the next snow storm!


I would crawl under the front axle and look for any vacuum hoses or electrical plugs that might have come loose. This is assuming you have automatic locking hubs.

Do you have a manual or auto transfer case? Do you have to shift or push a button for 4WD? Is the 4WD light coming on? Can you get 4WD high or low?

On some vehicles you have to go to 4WD and drive a little before things lock in.

With the 4WD on, can you rotate the front drive shaft by hand? Get someone to keep the truck secure while you're under there.....

Hi MrGadget,

It's all automatic. I just push a button on the dashboard and it goes into 4WD.

For 4WD LOW I just need to be stopped or rolling very slowly and in neutral, then push the "4 Low" button.

But, nothing's working now. So, I think I'll try your vacuum hose investigation first. Thanks!

Insta-Trac is an electrical system. I would guess either you blew a fusible link under the hood, or your switch on the dash is bad.

I'm not too familiar with later model GM, but most have some sort of transfercase shifting motor. Usually vacuum operated. I would look for a linkage on the T-case, then look for the actuating motor. Then have someone shift it in and out while you watch. Make sure it is moving. If not, look for the source. If vacuum, check your vacuum source and lines. Most of the GM's I have seen have some sort of front diferential disconnect. I.E. it disconnects the axles so they may free wheel. Anyway, these have an electric operated switch. These switches are notorious. So see if you can turn the axle by hand. This is sorta like a automatic locking hub, just works in the center. Look on the site of Look for links to GM, and technical articles. There may be something there that will help you.

See if you hear any sounds when you push the button to get into 4x4. In fact, have someone stand outside either in front of the vehicle, or to the sides of it, and see if they hear any sounds. Usually when the system engages, you should hear a click, or a clunk, some kind of sound to know that it goes in.

The GM IFS system is notorious for vacuum line failure, and they're the kind of thing that always fails at the worst possible time. Oldmanb77 pretty much hit the system dead on, and like everyone says, its probably a vacuum line thing. If not, check your electrical connections, then mechanical connections.

Shoulda gotten a dodge... :applause:

shoulda gotta dodge......

dear thumper talk, I have a dodge and the transmission stopped working. what do I do?

80-90% of late model GM 4x4 actuators go bad on frt axles,some also need

wire harness to hook up new style actuator pn#----0073 Sorry,I dont remember exact part # but call me @work tomorrow with the last eight of your vin# and I'll give you all necessary info.I' ve been in GM parts since

1976. 1-800-242-0155.BTW when its 8am your time it's 11am my time. :applause:

this may sound strange.....IF it does make a noise (you WILL hear it when you press the button BTW) and the 4WD doesnt engage, push the button then go backwards (put it in reverse and back up slowly). If no noise, the problem is a fuse or vaccum line. BTW a Toyota is the only 4x4 that is trust worthy. And im sure your dodge will go in 4WD, but will the tranny work afterwards?? i know my GMC will!! LOL.... :applause:

Our 1997 Suburban was famous for electrical problems and my understanding is that was not uncommon. Wouldn't be surprised if yours was an electrical problem. :applause:


Thanks for all your replies everyone. :bonk:

I'm going to check for any obvious issues like a vacuum line that's disconnected. If I can find anything, I'm probably going to just take it into the shop because I'm a crappy mechanic when it comes to electrical components, etc. :applause:


mine just did the same thing last week, it was an electrical problems took about 2 hours to get fixed at the shop.

The dash buttons are a very common source of problems.

2nd thing to look for is the actuator on the side of the transfer case.

When it's in 4wd and stopped, can you manually spin the front driveshaft? On mine, I can when it's in 2wd but not 4wd.

The front diff is non-locking on all GM trucks.

Is it Auto-Trak or a regular transfer case? The dash buttons do not tell you this... my 2500 is a regular transfer case, but it's electrically actuated from dash pushbuttons.

Probably your dash mounted t-case mode switch. Hit the dash above the switch and if the LED's flicker it will be the switch. Does your service 4X4 light come on? Are the LED's lit? I've replaced piles of these switches in the '99 to '01's I think they rectified the problem in '02. There are no vacuum lines on this system at all. If it's not a switch, unplug your front axle actuator and do pinout tests on the front actuator confirming powers and grounds. The system consists of the dash switch, 4 wheel drive module, encoder motor on the transfer case, and front axle actuator. The front actuators are now very reliable since they went away from the old design so my guess is it isn't it. There has been some trouble with the encoder motor positon switches but you would have to scan it to see what codes you have. These systems are very simple and if you took it to a dealership they should be able to diagnose it in minutes with a scan tool.

Don't trust spinning the driveshaft by hand diagnosis on the auto-trac (if that is what you have). They have adjusted clutch pack preload various times depending on year and VIN break point. Some you can spin by hand, and some you need a prybar because of the preload.

An auto-trac transfer case will have a 4 button dash mounted switch (auto,4hi,2wd,4lo). A non auto-trac will have a 3 button switch (4hi,2wd,4lo). Another way to tell is if you are under the vehicle, look at the rear extension housing on the t-case. If there are 2 speed sensors, it is an auto-trac.

My guess is the switch. Let us know how you make out. :applause:

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