2004 Trailblazer Transmission

For the most part, but 2004 trailblazer transmission is a carryover from the 2003 trailblazer transmission.  The Trailblazer utilizes the 4L60E transmission in all models.  The 4L60E is very capable in these trucks.  With the trailblazer, it’s more likely that the engine will fail before the transmission does.  The exception to that would be any Trailblazer with a LS-series V8.


What kind of transmission does a 2004 Trailblazer have?

The 2004 trailblazer uses the 4L60E.  It doesn’t matter what type of engine that is in it either.  The main differences between the different transmissions in the various trailblazers are going to be whether or not it was equipped with four wheel drive.  If it does have four wheel drive it’s going to have a transfer case.  The 2×4 and 4×4 transmissions are not easily swapped for one another.

It is very much worth noting that the non V8 version of the ’04 Trailblazer uses a different bellhousing than the V8 version found in most GM trucks and the Corvette.  Here’s more on 4L60E Identification.

It is easy to confirm the type of transmission in your Trailblazer is a 4L60E.   Go ahead and open up the glove compartment.  There is a sticker right inside there that’ll tell you all of the important things that your Trailblazer was originally equipped with.  The code you are looking for is going to be M30.  If you are interested in finding more about what else your truck is equipped with, here’s a complete list of Trailblazer RPO codes.


2004 Trailblazer Transmission
You can see the RPO code M30 clearly in this picture. This is proof positive that this vehicle is equipped with a 4L60E.


2004 Trailblazer Transmission Problems

As mentioned above the ’04 trailblazer uses the 4L60E transmission exclusively.  It is generally a very reliable.  Like any mechanical device though, the 4L60E will develop problems with age and mileage.  This section aims to cover typical 4L60E as well as a few 2004 Trailblazer specific problems as well.

While the information below is meant to be broad and useful. If you want more detailed info, check out 4L60E transmission problems for help diagnosing problems that are specific to this one transmission.


Low Transmission Fluid

Before going anywhere with your transmission problem diagnosis, go ahead and check your Trailblazer for low transmission fluid.  Having low fluid is enough to cause all sorts of problems.  Including:

  • Overheating
  • Shuddering
  • High Engine RPM

Here is way more on low transmission fluid symptoms.  You’d be surprised.  Just take a look. If it is low, you’re doing further damage every time you hit the road.  It always makes sense to start with the most simple thing first.


Torque Converter Won’t Lock

If you feel like when you drive your Trailblazer and the RPM just seems to be a bit higher regardless of how fast you’re going, but espescially highway speed, it’s a pretty good indication that the torque converter is not locking.

This is usually caused by a switch that strikes the brake pedal.  This switch is prone to going out on Trailblazer’s.  If you know how to use an electrical test light than it’s a very easy diagnosis.

It’s the exact opposite how the break light switch works.  The switch breaks the circuit.  What that means is when you push the brake pedal the torque converter unlocks.  That way if the switch fails you don’t end up with the converter stuck in the locked position.


Limp Mode

Limp mode occurs when the ’04 Trailblazers’s computer system determines that there is a catastrophic issue.  It’ll only allow the vehicle to go into one forward gear and reverse.  A lot of the time it’s cause by the computer not receiving any signal at all from the transmission.  

A good place to start with limp mode is to take a look at the wiring harness.  It plugs into a 4L60E on the passenger side above the pan.  Here’s a picture to help you get an idea:


2004 Trailblazer Transmission Problems

Once you have located the harness plug, make sure that it’s seated nice and tight.  If it is go ahead and take a look at the harness itself and see if you can find any wiring that looks like it’s damaged or frayed.  These trucks are fifteen years old now.  That’s a lot of time for the elements to do their job.


Wiring Harness

As mentioned above, a shorted out or broken wiring harness can leave your Trailblazer unable to talk to the transmission.  When this happens it’s more than likely going to enter limp mode.  It’s worth taking a look.



If you feel like your transmission is slipping there are several issues that may be causing it.  Most of them involve a lot of money to fix, because they involve opening the transmission case.  If you feel like your transmission is slipping, it may be a good idea to check the fluid.  You may get lucky and find out that you just need to top it off.

For more on this, please check transmission slipping diagnosis.



The 2004 Trailblazer has a fantastic Transmission in the 4L60E.  You aren’t very likely to have many problems that will arise from it.  If you feel there’s anything else that could be added, feel free to leave a comment and I’ll update the article.