4 wheel drive

Hey guys, just alittle explaining and then question
I have a 99 Yukon z71, I CANNOT get the 4x4 to fully engage, I have replaced the transfer case and know that’s working strong I’ve replaced the motor on the differential and just today 2/19 replaced the front diff and now…still nothing, off the ground the front tires will spin but not strong but on the ground freakin nothing still
Now my question is, I have a wire ripped out of the front hub assembly so no abs oh well so would that be causing that to not work as everything else works, mind you I can hear that motor on the diff move smoothly
I could really use you help as I’m about to run it of a bridge thank you in advance

I had water in the connector at the 4wd actuator at the front diff. It shorted the actuator. Pull off the plug, inspect, and put a multimeter across the contacts. When you shift it to 4wd you should get around 12vdc. If that’s good maybe lazy or toasted actuator. Mine is the thermal one that takes 5 Mississippi to kick in, after I cycle the floor shifter. Yours is probably the upgraded one. I fill my connector shells with DC4 dialelectric grease at the undercarriage now.

they used the thermal front axle actuator for quite a while and are known to fail. they will either just stop working or start popping fuses. also yours has push button 4wd and that dash switch is a fail point also.

Yeah I have done replaced all that, cleaned contacts put dielectric grease on everything and everything’s working except it won’t lock the front diff all the way in, I have even replaced the bottom on the inside of the truck, I just didn’t know if the abs wire being ripped out would cause it not to fully engage because it can’t real the wheel speed maybe

Sorry not bottom but button switch

You should get that ABS wire repaired. Maybe there is some logic there.

Hi Daddyj! I had a problem with 4WD engaging, but intermittent - only once in a while, so I assumed it was an electrical or grounding issue. One YouTube video showed ‘super grounding’, assuming you’ve checked all wires and harness connections, maybe try this simple and cheap fix.

On the drivers side inner fender runs a 4WD wire harness with a connector mid-point. I spliced a 2 1/2 ft piece of 16 ga. wire to the existing black wire (ground) of this harness (before or after the connector plug, doesn’t matter), then ran the other end of this ‘new’ ground wire to a ground connection on the firewall (lots of points to choose from). This worked well, my 4WD (H, L, AWD) worked fine for about a year ... until the Transfer Case Motor encoder sensor gave out, lol


Only thing I’d recommend before doing this is disconnect battery or pull fuse before starting.

I’ve also heard a wire harness runs over the front axle near where the Actuator is. Sometimes the harness wires can rub bare - so they need repair, and of course the Actuator may need replacing.

Cheers, Dwayne

Check for power at the front axle actuator when you activate the 4wd. If you have power and ground the actuator should be engaging the front. Shouldn't have anything to do with the ABS wire, my 98 hasn't had wires from the ABS sensors for 10 years and 4wd works fine. The actuator on the axle moves a fork that engages the right axle unless something inside there is broken it's most likely the actuator.

Success?