Chevy Trailblazer 4x4 Not Working? Four-Wheel-Drive Actuator Problem Symptoms

Updated on December 6, 2016

Actuators and Encoders and Solenoids, Oh My!

It all started with a 4-wheel drive switch. My husband was driving our 2005 Chevy Trailblazer, and when he went to change the switch into 4 wheel drive, the switch wouldn't budge. Instead, it broke off--through no fault of my husband I'm told--and thus began our massive 2013 hunt for what's-wrong-with-the-Chevy-4WD (not to be confused with the-Chevy's-brakes-are-still-squeaking-after-we-changed-pads-and-rotors 2012 fiasco). I decided to write this article because I've learned far more than I ever wanted to know about Chevy vehicles in Chevy forums from so many others who have written about their own Chevy issues. Perhaps this hub will help other folks with the same symptoms jump straight to the source of the problem instead of taking the long route. And yes, there really is a Trailblazer forum you can join at

AC Delco Actuator with Encoder Motor

Symptoms of Encoder Motor Failure

Other vehicles may be different, but on our Trailblazer the symptoms were that the "service 4WD" light was on, lights on the switch would blink and then remain steady, but the truck wouldn't shift into four wheel drive. No noises could be heard underneath, as if it wasn't even trying to transfer. We thought it was a switch issue (and it was the cheapest fix), so we bought a $28 4-wheel drive dashboard switch from the stealership and popped it in. We still had issues. We read on several forums that the #8 fuse in the front and #45 under the rear driver's side seat often need to be pulled for a minute to reset the transfer case module. So we tried this, but it still had issues.

Give DIY a try?

Our eBay Actuator

At this point, we were saddened to realize that we might actually have to shell out substantial money to fix this problem. Upon further research, we found that many folks were finding success in replacing the front actuator. Here is where it becomes confusing! We found one on eBay and patted ourselves on the back for only having to pay around $100 to fix this potentially pricey problem. NO. After that didn't work (thank goodness for "returns accepted" policies on eBay), we took it to a shop. They read it with their nifty high-tech Chevy scanner tool and claimed it was indeed an "actuator" problem. Upon even further research, we found that the words "actuator" and "encoder" were used interchangeably on many websites. We once again patted ourselves on the back and bought a $150 Dorman encoder motor on Rock Auto.

NO! Not only did it not work, but the rig didn't even recognize it at all--none of the switch's lights would light up.

Finally, the Answer

Luckily, my dad has a buddy who owed him a favor. After taking a look, he said he had seen aftermarket encoder motors fail to work, and that an AC Delco actuator might do the trick. Come to think of it, I did see that written in a forum somewhere once upon a time, but failed to find enough suppporting evidence to back that up. We bought our final part for $200 out-of-pocket, made sure it said "AC Delco," and collectively held our breath as we popped it in. Sure enough, it did the trick. No more service light, no more non-moving switch mode light, and we can hear the rig shifting when we turn the switch. Now if we can only figure out why the driver's side headlight keeps burning out every few months...

Have You Had Encoder Motor Failure?

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    • profile image

      Jeff Williams 

      2 months ago

      Thank you Holly so much for this post. I've been driving myself crazy trying what to do and what to buy. Because of you I get it now.Thank you.

    • profile image

      Chevy 04 

      5 months ago

      I also found my TB doing the same thing in the article Holly wrote. Saved my self $521.45. Picked up actuator/encoder moter at junk yard for ten dollars. Put it in and 4wheel and it works. THANK YOU to Holly and the article she wrote.

    • profile image


      6 months ago

      I have a 2002 LT Trailblazer that won't engage in 4 wheel drive. You turn the switch and you can here the actuator but it doesn't lock in 4 wheel drive

    • profile image

      Jesse Vigil 

      13 months ago

      I have a 2005 Chevy trailblazer and it will not go into 2 hi. What is the problem?

    • profile image


      17 months ago

      Your Headlights will continue to burn out. Anon is correct that the Pigtail is the right fix. However, just because it happens to a lot of TB's doesn't mean it is normal. There is definitely a reason (Bad ground, wrong gauge wire, poorly designed loose connectors, Ect) I installed LED bulbs and I also changed the pigtail's. The new bulbs are brighter and do not even generate anywhere near amount of heat at the connector the standard bulbs did.

    • profile image


      3 years ago

      I have a 2003 trailblazer 4.2 motor it is surging when driving ..And another problem the 4x4 wont engage light is on but nothing happens when I turn it to 4 low or all 4 but the light is on each time I change it from one to another help pl

    • profile image


      3 years ago

      Free Fix!! I have an 04 Trailblazer. When it is cold outside, sometimes when I start the TB, the lights on the 2wd/4wd selector switch flash for 10-15 seconds and then go out. The TB will then NOT go into AWD, 4wd, etc. here's the fix. When you start the vehicle, push the brake pedal and quickly shift the gear select into neutral. The lights on the 4wd selector switch will then lock solid and work. I live in the snow belt so I know this works. I am thinking that the Actuator is having a syncing/positioning problem. This will override the issue.

    • profile image


      3 years ago

      My four wheel drive only works when its cold outside. What could cause it to not work when warm. 02 trailblazer

    • Boisegal profile imageAUTHOR


      4 years ago from Boise, ID

      Very cool! Glad I've helped someone!

    • profile image


      4 years ago

      This article was way cheaper then taking to a mechanic!! I ordered the part from the link above. I put it in after watching YouTube University. And now my 4Wheel is up and running like new. Thanks Very much for sharing your story!!

    • profile image


      4 years ago



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