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Chevrolet Silverado 1999-2006: 4WD Diagnostic Guide

The heart of your off-road enjoyment is the 4WD, which will get you from point A to point B no matter the terrain. So if your Chevy Silverado is showing symptoms of a slipping 4WD system, continue reading for common diagnoses and repairs.

By Brett Foote - June 19, 2015

This article applies to the Chevrolet Silverado GMT800 (1999-2006).

4WD systems give truck owners unprecedented abilities when it comes to gaining traction, both on and off the road. But like most "upgrades," these systems also consist of numerous components, which over time will wear out and cause problems. Like any truck, the Chevrolet Silverado has its fair share of known issues in regard to the 4WD system. Keep reading as this article will go over some of the more common ones, along with information on how to fix them.

Step 1 – Check for bad axle actuator

If your truck is driving perfectly fine but switching into 4WD doesn't engage the front wheels, you might have a bad axle actuator. Replacing the actuator is pretty easy and inexpensive. You can find a new actuator online at prices ranging between $65 to $100.

To replace the actuator:

  • Simply unbolt the skid plate underneath your truck, and unplug the wire harness connected to the back of the actuator.
  • Using a pair of slip pliers, turn the actuator counterclockwise and then remove it by hand.
  • Now just screw in the new actuator clockwise, plug the connector back in, bolt your skid plate back on, and you're good to go.
Figure 1. Replacing an axle actuator with slip pliers.

(Related Article: How to Replace 4WD Axle Acutator - ChevroletForum.com)

Step 2 – Check for selector switch failure

The selector switch is a known issue with these trucks, which is largely attributed to bad solder joints. You will know when the switch is bad if it doesn't illuminate, respond to any button pushes, or if you get a code. Replacements are available for around $30, or you can try a DIY fix by taking the switch apart and re-heating all the solder joints on the back circuit board to ensure proper contact.

To remove the selector switch:

  • Lower the steering wheel all the way down.
  • Put the truck in gear.
  • Then, gently pull the dash off to gain access.
Figure 2. Selector switch in a Silverado 1500.

Step 3 – Check for transfer case motor failure

A bad transfer case motor will often throw a code on your dash, but can also be diagnosed if you fail to hear the motor spinning once the 4WD gear is engaged. A new transfer case motor will cost you around $200.

To replace a transfer case motor:

  • You must drop the front drive shaft. This is a difficult job as, oftentimes, these components are rusty and hard to remove.
  • Then, remove the skit plate to allow you to remove the drive shaft.
  • Once you unbolt the drive shaft, remove the electrical connectors attached to the transfer case.
  • Remove the three bolts holding the transfer case motor in place, and then install the new motor.
Figure 3. A worn transfer case motor.

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Other Possible Issues

  • Blown fuses are a simple fix, and there are fuses in both the engine bay as well as the cabin that control various 4WD components.
  • There is a grounding wire underneath the driver's side compartment on the chassis, so always check and make sure that the ground is making contact with metal.
  • The 4WD control module is located deep within your dashboard, and is very difficult as well as expensive to replace. On occasion, they start to go bad, generally causing 4WD to not engage and without any codes being thrown. But if you are getting a code, the problem is still likely not your module.

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