03 Suburban Front Axle won't lock in 4wd

I have a friend who has a '03 Suburban and it won't lock the front axle in AUTO, 4HI or 4LO.

The switch on the dashboard looks to be working properly.

It engages the transfer case into 4LO, but only drives the rear wheels.

I scanned his computer with my Snap-On 2500 "Brick" and don't see any trouble codes but I see two things that may help figure out what's wrong.

F AXLE SW LCKD = NO
FRONT AXLE REQ = NO

Both of these show YES on my 01' Tahoe when in AUTO, 4HI or 4LO

Both propeller shaft RPM outputs are working and same RPM going down the road.

I'm thinking it's a bad electrical connection to or bad front actuator motor since it worked a couple months ago when he bought the truck.

Am I on the right track?

Am I on the right track?


from your vehicle discription of malfunction I would guess the encoder motor is bad...

the front diff actuator locks the front axles to each other PERIOD......

THE TRANSFER CASE ENCODER MOTOR engages the front to rear...

with a drivetrain scanner get the oem DTC's and with that ,,, I can better find out, what it is, most likely..

Unfortunately there are no DTC's in the Auto Transcase or Transmission sections.

If the encoder wasn't working, wouldn't it not go into 4LO like it is doing but he only gets 2LO because the right front transaxle is not locked to the left side?

Unfortunately there are no DTC's in the Auto Transcase or Transmission sections.

If the encoder wasn't working, wouldn't it not go into 4LO like it is doing but he only gets 2LO because the right front transaxle is not locked to the left side?

to be sure what's wrong the drive train DTC'S must be pulled...this could be other things defective..the encoder motor is usually what causes the loss of 4WD...

place the drive train switch into auto 4WD...are the front axles locked to gether ? lift vehicle off ground both front wheels to test..

if the wheels are locked then it is a transfercase/encoder motor/control problem..DTC will show were the problem is located..

We didn't lift the tires off the ground, but we do know that it is not "tightening up" the front end like a vehicle would if you locked the hubs on an old 4x4.

Also the "encoder sensor" readout on my scantool was saying that the transfercase was shifting and again it was shifting into the lower gear but only driving the rear wheels.

We didn't lift the tires off the ground, but we do know that it is not "tightening up" the front end like a vehicle would if you locked the hubs on an old 4x4.

Also the "encoder sensor" readout on my scantool was saying that the transfercase was shifting and again it was shifting into the lower gear but only driving the rear wheels.

since you refuse to follow my directions good luck..

haha well he was here last week when we had a lot of snow and we weren't going to crawl under the truck then and it's hard to do it now that i'm in virginia and he's in south carolina and doesn't have a jack. he will be back in a couple weeks and we will continue troubleshooting then.

in the meantime, has anyone else run into this problem?

If your transfer case has Auto button the clutch in the transfer case could be bad. Mine was bad had to replace the entire transfer case. The Auto TC needs the blue AutoTrac II fluid or it will burn up.