How to test a chev front differential actuator

There is an actuator motor located on the transfer case. It selects range; hi neutral and lo and engages the front differential. There is a second clutch actuator motor on the front differential that engages the front wheel hubs.

You will need to disconnect both motors to eliminate electronics. It could also be you have an abraided wire to either the transfer case or the front differential. If unplugging both actuators doesnt stop fuse blow, you will need to test for signal or power to ground shorts.

Free (with ads) schematics are available using the "carmin std" app.

The actuator will not be on the front differential or drive line, it will be on the transfer case, which is mounted behind the transmission. Follow the front drive shaft back from the front differential, and the component at the rear of the driveshaft is the transfer case. That is where four wheel drive is engaged/disengaged.
I'm not familiar with your vehicle, but if you have a separate lever to engage 4wd, there will not be a fuse for the actuator - it is a manual system. If the 4wd is selected electrically, check that all wiring and connectors on the transfer case are in good condition.

Check for power to the front differential actuator. This actuator slides a gear in position to lock the differential to drive the front wheels. If you have power and ground to the actuator when in the 4HI position, the actuator has gone bad.The 4LO is only engaging at the transfer case, but the front wheels are still not engaged if it is not working in 4HI.

There is an actuator located in the front differential " About 15 minutes to change " . By transfercase actuator , do you mean the Encoder Motor " transfercase shift motor ? 9 times out of 10 it is either the front differential actuator or the transfer case encoder motor

First check plug on actuator on front differential and be sure that plug is securely fastened to sensor and that plug has no rusted or corroded pins. Then test actuator and be sure it is operating properly. More than likely your four wheel drive actuator is malfunctioning.

Make sure that the vacuum hose connector is connected AND connected correctly at the transfer case and at the front differential. If that is all right and the front differential still doesn't engage, then you need to test the vacuum actuator at the front differential.

It sounds like your front 4x4 actuator on the front differential has locked up. It's common to happen and the fork that engages the 4X4 in the differential is still locked up or partially locked up.
On the full size, the front actuator is electric, not vacuum.

When in 4wd mode, a switch on top of the transfer case conducts 12 volts out to the actuator. Wire #50 (brown) is the 12v feed, and it conducts to the light blue wire (#900) to the actuator.
When shifted out of 4wd, the switch opens up and no voltage goes to the actuator.

Check voltage at the connector for the front actuator (at the front differential - it looks like a large bullet that threads into the front diff.) If it has 12 volts, the actuator is the problem. If it does not have 12 volts, check the transfer case switch and the power feed to the transfer case.

I'll assume it is the actuator, if the plug to the actuator is getting 12 volts when in 4wd.
The way this actuator works, is it is a sealed chamber that gets heated by voltage. When it heats, the pin in the end swells and pushes a shift fork in the front differential. The shift fork engages a spline on the passenger side of the differential, and boom! you have 4WD.

GM offered an upgrade to this actuator that is a motor instead of a heated device. However, it requires a small harness addition, a spacer, and a new actuator. It is about a $150 to $200 option.

If I were you, I would buy a new heated actuator. They are available at most auto parts stores, and are about $90. They are also on eBay for about $55 plus shipping. These are very easy to change - just thread out the old one, and thread in a new one.

Good luck. The actuator is usually the problem 90% of time but recheck all of the wire harness just to maker sure there is no short before replacing any parts.
http://www.getdieselpower.com/misc_auto/actuator_upgrade/GM_TRUCK_4X4_ACTUATOR_UPGRADE.html

There is a switch on the transfer case that likes to go out on these, they are about $15 or the front differential actuator is bad, the actuator is the round cylinder that is screwed in under the front diff, both very easy to change

On the front differential there is a thermal actuator. It engages your front differential. In parts catalogs they are called 4wd actuator. they are not easy to replace.

I have a 1999 chevy blazer that stuck in 4 wheel drive. How do you get it out.