Chevy 4WD Troubleshooting (With DIY Methods : 2023)

This article includes an in-depth section on Chevy 4WD Troubleshooting.

Tracking down any issue boils down to testing hundreds of times since there’s just so much that could’ve gone wrong with the 4WD system.

For example, you might have damaged wires underneath the driver’s side, or the encoder motor is toasted.

Either way, we’re here to help you get your truck back on the road.

Just keep in mind that troubleshooting is relatively simple, but it can take some time if you’ve never done it before.


Top 08 Common Chevy 4WD Problems

The 4WD system in our cars is pretty effective and can work for years without causing much trouble.

However, there’s just that one time where everything seems to go down the toilet.

Don’t worry, though. Here are the most common problems found on the Chevy:

01. Truck Struggles When Switching to 4WD

Truck Struggles When Switching to 4WD

Apparent problems with the four-wheel-drive mode are usually related to some issue in the encoder motor.

When there’s something wrong with the encoder motor, drivers will have difficulty switching to 4WD.

Sometimes, you won’t be able to switch from 2WD to 4WD at all. You can still operate the vehicle in 2WD.

But, if you are in a snowy area, not switching to 4WD is a huge deal.

That said, follow this troubleshooting procedure:

  • Generally speaking, when there’s something wrong with the 4WD, it’s related to the sensor built into the encoder motor. So, to test it out, pull out your OBD scanner. If the sensor is not working, you will get the following code: “C0327.”
  • Alternatively, if the sensor failed, the service four-wheel drive light should appear on the dashboard.

Replacing the sensor should be more than enough to get the truck back in great shape. However, if that didn’t fix the 4WD issue, replace the encoder motor.

MORE: Chevy Truck Blower Motor Problems

02. Chevy 4WD Selector Switch

Many Chevy owners experience issues with the 4WD. Sometimes, they get on the truck, and the moment you turn the gear selector to the 4WD mode, nothing seems to work.

The light will flash, but the vehicle does not switch to the 4WD mode.

Presumably, the issue is related to the shifter module. That said, here’s a list of standard codes you should get if the shifter module is the culprit:

  • C0387-59
  • B0790-06
  • U0140-71
  • U0121-71

If you’re getting those codes, here’s how you can find the shifter module:

  • The component is located just underneath the kick panel, so you’ll have to remove the screws holding it together. Once that’s done, remove the fuse box cover.
  • From there, lift up the parking brake handle and then remove the bolt. Now that we have settled that, you should be able to pull the kick panel.
  • As you might have noticed, it’s pretty dark in there. So, go ahead and get a flashlight.
  • That said, the shifter module is mounted on the back. Reach your hand and then release the clip holding it together. After that, it will come right off.

Be careful when installing the new shifter module as it has a few panels inside that can easily get damaged. If you bent them, you’d run into the same issues.

When pushing the plugs inside, you may bend the panels. Watch out for that.

Before replacing the shifter module, use your scanner to reset the transfer case problem.

Otherwise, if you turn the gear selector, it won’t work.

However, if you don’t have a scanner at home, here’s the process to pull this off without one:

  • Disconnect the battery cables. After that, leave the vehicle in neutral. From there, pull the wires together and connect them with a pair of vise grips. Keep holding them for roughly 25 minutes.

The whole idea behind this process to reset both the BCM and ECM. After going through the steps, the gear selector should work like before.

03. Light Keeps Blinking

Another issue we’ve run into is that the gear selector light keeps blinking when switching to 2WD or 4WD.

But they don’t work at all. If you start up the vehicle, you’ll get the four-wheel service light on the dashboard.

What’s more, we’ve come across drivers that claim the truck engages only into low gear. But even then, the front shaft won’t turn.

So, what is the culprit? Well, chances are the wires underneath the driver’s side got cut off. That said, here’s how you can fix the problem:

  • Get underneath the driver’s side. Right underneath the edges, you should be able to spot a couple of cables. Here, you want to diagnose the wires. Perhaps, there’s a wire poking out.
  • If that cable is not plugged in, there’s no way for the 4WD to work. So, go ahead and grab that wire and put it back on.

04. Loud Noise Under The Truck

Heard a loud noise coming from underneath the truck the moment you stepped on the pedal? Well, perhaps you’ve got stripped splines inside the rear output shaft.

However, it’s hard to tell as you could also have a broken transfer chain inside. If the chain is the culprit, you will also hear a squealing noise.

That said, the best way to determine if it’s the transfer chain or the splines inside is to pull the transfer case and then open it up and inspect the inside.

Noise is a clear sign that there’s something wrong with those two, but that alone is not enough to confirm the culprit. As for the splines, pull the shaft to confirm the problem.

MORE: Can You Drive With a Broken Transfer Case

05. Chevy 4WD Actuator Fuse

Chevy 4WD Actuator Fuse

Similar to other problems we’ve covered so far, this time, the service 4WD light stays on the dashboard. If this is your problem, maybe the ATC fuse died out.

If the ATC fuse is the culprit, the service 4WD light will flash as soon as you start up the truck. This occurs as the ATC fuse is connected to the 4WD system.

Luckily, replacing the fuse is pretty cheap and easy. That said, here’s how you can troubleshoot this problem:

  • Pop the hood of the vehicle. After that, find where the fuse box is. Next up, find the “ATC 20A” fuse. If you don’t know where that is, find the chart on the fuse box. This manual explains where every single fuse is located.
  • Once you’ve found the “ATC 20A” fuse, go ahead pull it out using a fuse puller. Alternatively, use a set of pliers.
  • If you take a closer look inside, you’ll notice that there’s a small silver piece inside. If you have a blown fuse, the little metal part will look like it was split in half.
  • A good fuse should not look like this. Instead, the little metal inside should be connected, not split in half.

Typically, the fuses inside the fuse box stop working when they’re exposed to cold temperatures.

But like we said before, replacing the “ATC 20A” fuse is super cheap. So, you won’t have to take the car to the dealer.

06. My Car Is Leaking Fluid

As you know by now, Chevy 4WD troubleshooting can take a lot of time as there are just so many things that could have gone wrong with your truck.

But this time, you could have a leak on the tail-shaft seal. Diagnosing whether the tail-shaft seal is no longer working is pretty straightforward.

  • Get underneath the vehicle, and you should see a puddle of liquid. Get closer to the tail-shaft seal, and you’ll probably find liquid residue all over it.

As expected, you’ll have to get a new one. Don’t worry, though. It’s pretty easy to replace the seal. For this, you’ll have to pull the driveshaft and then remove the old seal. After that, install the new one in, and you’re good to go.

07. Four Wheel Drive Noise

If your tires are wearing unevenly, that’s why the vehicle makes so much noise when switching from 2WD to 4WD.

That said, below you’ll find how you can tell that the tires are wearing unevenly:

  • Carefully look at the tires. For example, the thread of the tire could go down in the middle and then back up. That’s an obvious sign of uneven tire wear.
  • Alternatively, take a good look at the tire wear indicators. Just in case, the tire wear indicators are those small pieces of rubber between the tire treads. So, if the wear indicators are even with the tire treads, it’s time to get new tires.

There are many reasons why your tires are wearing unevenly, including worn-out shocks and struts.

When these two get damaged, the vehicle will bounce up and down when it is in motion. So, when going down the road, there’s an abnormal amount of pressure on certain points of the tire caused by the shocks and struts.

Other culprits that can wear your tires are ball joints and springs.

Either way, the tires must be replaced to eliminate the grinding noise. If you want to know more about uneven tire wear, go check this video out:

Tire Wear Patterns And What They Mean?

MORE: Subaru Tire Pressure Sensor Problem

08. Chevy 4WD Light Not Working

Chevy 4WD Light Not Working

Finally, one problem we’ve seen among Chevy owners is that the gear selector’s light does not work. This is not a big deal as the 4WD probably still works, but it can be annoying when the fixture fails to flash.

With that being said, here’s how to troubleshoot this problem:

  • Crawl underneath the truck. Next up, find the wires from the front differential until you reach the transfer case.
  • When tracing the wires, you should find a switch on the transfer case. If you move a little closer, you should also find the switch on top of the TC. That’s the switch that sends power to the four-wheel-drive system
  • If the wire got corroded, the light on the gear selector would not work, and you’ll have a hard time switching to 4WD. So, to fix this issue, clean the plug, and everything should go back to normal.


Below, we’ve narrowed down the most common questions about the 4WD system on Chevy vehicles:

1. What would cause my 4 wheels drive not to work?

There are plenty of reasons why the 4WD system is not working. Perhaps, you got a blown fuse, or there’s something wrong with the sensor built into the encoder motor.

2. Why does my 4WD light stay on?

Pop the hood of the vehicle. After that, find the “ATC 20A” fuse inside the fuse box. Pull it out and install a new one. Most of the time, if you’re getting the 4WD light on, there’s something wrong with the fuse.
Alternatively, check that the sensor inside the encoder motor is still in great shape.

3. How can I tell if the transfer case is about to die?

When the seal in the middle of the transfer case and the transmission goes bad, transmission fluid will get inside the transfer case. Another problem you should be aware of is pinholes.
Those tiny holes on the transfer case are quite hard to find, and you’re probably losing fluid because of them.

4. How much does it cost to fix a four-wheel-drive system?

It’s difficult to answer as some problems regarding the 4WD system might not be as expensive. For instance, you could have a damaged fuse, which costs about $20 to replace.
But at the same time, you could have a lousy transfer chain, which costs roughly $300.


Chevy 4WD Troubleshooting is super easy, and you can do it at home. When trying to find a problem, always start with the easy stuff.

Drivers often go all-in when tracking down an issue only to realize it was a fuse messing up the four-wheel drive.

Also, when troubleshooting, don’t throw parts at it just for the sake of it.

Spend enough time finding the issue before replacing anything.

This is a rookie mistake, and you don’t want to spend hundreds of dollars on useless parts.

Now that we have covered the entire troubleshooting guide. We hope you managed to find the culprit.

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