2001 Yukon XL 4x4 only works when truck suspended in air

[saltednuts]

2001 Yukon XL SLT 1500 5.3

 

4x4 works when truck is jacked up on a lift (all tires are suspended in the air) however when the truck on the ground, the 4x4 isn't working. The rear tires have power yet there is nothing coming from either of the front tires. Anyone else have this issue??? I have taken my truck to a mechanic twice now and they have no idea.

[NitroCherokee]

You won't really be able to see it fail. It's easy to change if you are semi mechanically inclined. If you just have a little do it herself tool kit and have only changed your oil take it to a shop

[saltednuts]

Ok thanks. With the hundreds that you've switch out, did the vehicles have the same situation as mine where on the lift all the wheels received power, just not on the ground? I'm thinking of purchasing the part and having my mechanic install it, yet I rather not purchase a part and pay for labor and it doesn't fix it. Obviously, you can't be sure but you seem to now what you're talking about.

[NitroCherokee]

Ok thanks. With the hundreds that you've switch out, did the vehicles have the same situation as mine where on the lift all the wheels received power, just not on the ground? I'm thinking of purchasing the part and having my mechanic install it, yet I rather not purchase a part and pay for labor and it doesn't fix it. Obviously, you can't be sure but you seem to now what you're talking about.

Yes, first one I had stumped me I had it in the air and 4WD engaged took it out in the icy parking lot and just the rears would spin. I'm 97.7% sure it'll fix yours. The lift thing is something I used to help diagnose the 4WD concerns in the dealer

[saltednuts]

Yes, first one I had stumped me I had it in the air and 4WD engaged took it out in the icy parking lot and just the rears would spin. I'm 97.7% sure it'll fix yours. The lift thing is something I used to help diagnose the 4WD concerns in the dealer

Awesome. Thanks for the help. I'll update once I have the part replaced.

[sahls01gmc]

Will I be able to verify the 4-pin or 6-pin motor based on my VIN and the RPO codes? Or should I probably take the 5 minutes to crawl under and look?

[NitroCherokee]

I would think by VIN, but usually the connector does not come out of the encoder motor very easy. I have had to carefully use heat to get it to come out before

[saltednuts]

Is the issue with the fronts not engaging occurring when you are starting from a stop and the truck is in auto 4wd?

The auto only engages if there is a wheel speed diffetence when all wheels are rotating.

No this is occurring in 4x4 High and Low and Auto as well

[gmtech4]

If your front hubs use vacuum, there could be a leak that is causing them not to engage fully (with the weight of the truck). Check vacuum line for leaks

Sorry no vacuum on chev trucks since a kazillion yrs ago ,,

 

Ford still does the dumb bastards

[gmtech4]

Ok thanks. With the hundreds that you've switch out, did the vehicles have the same situation as mine where on the lift all the wheels received power, just not on the ground? I'm thinking of purchasing the part and having my mechanic install it, yet I rather not purchase a part and pay for labor and it doesn't fix it. Obviously, you can't be sure but you seem to now what you're talking about.

Scan it first bud !! No guessing , ya can't return electrical parts

[[email protected]]

Sorry no vacuum on chev trucks since a kazillion yrs ago ,,

 

Ford still does the dumb bastards

Thanks for getting me to the 21st century. I still like levers and cables. Did fail as often. I also liked getting out and locking hubs. The more moving part added to any device the more chance of failure. I had a 98 Sonoma and it still used a vacuum actuator.

[Barnapkin]

Is the issue with the fronts not engaging occurring when you are starting from a stop and the truck is in auto 4wd?

 

The auto only engages if there is a wheel speed diffetence when all wheels are rotating.

[sahls01gmc]

My truck does the exact same thing. I have replaced the front diff actuator and dash switch, with the same results. I've had it scanned, but no codes show up. Perhaps they were not scanning it correctly. I haven't replaced the transfer case shift motor, but I'm not sure that is the problem either.

 

Every once in a while the "SERVICE 4WD" light comes on for a brief second when I start the truck, but always goes away and never comes back on.

[[email protected]]

If your front hubs use vacuum, there could be a leak that is causing them not to engage fully (with the weight of the truck). Check vacuum line for leaks

[NitroCherokee]

Replace the Encoder Motor. They have a "brake" in them that gives out and does not keep it fully engaged. I personally have probably replaced close to 100 of them for the exact concern

[kstruckcountry]

My truck does the exact same thing. I have replaced the front diff actuator and dash switch, with the same results. I've had it scanned, but no codes show up. Perhaps they were not scanning it correctly. I haven't replaced the transfer case shift motor, but I'm not sure that is the problem either.

 

Every once in a while the "SERVICE 4WD" light comes on for a brief second when I start the truck, but always goes away and never comes back on.

If the service 4wd comes up, there is a code stored. What scanner does he use?