Question about 2004 Chevrolet TrailBlazer

3 Answers

Service Engine Soon Light on a 2004 Trail Blazer

My SES light came on yesterday under what I would consider to be normal driving with no noticeable problems (at least to my untrained eye and ear)... I ran the OnStar diagnostics, and they told me they received signals indicating an error with ether transmission or power train.

Today, I called the Chevy dealer, and they want $100 just to run a diagnostics on it. Then the repair costs would depend on what they find.

Is there anything I can do prior to bringing it to the dealer to check things out on my own?

Much appreciated,

Posted by on

  • 4 more comments 
  • gromenesko Dec 04, 2008

    At this point, I'm very hopeful. I couldn't find the fuses labeled as you mentioned, but I did take the battery cables off (both though I know I didn't need to)... I also fittled with the gas cap and doubled up a gallon bag and put in in between the cap and receiver... with these two, the light stayed off for 2-3 minutes... I am planning to replace the gas cap, and pray that this is all I need to do...

    Thanks, you just saved me about $100 plus what ever some mechanic would come up with as possible things to try...

    Very much appreciated,

  • Anonymous Feb 09, 2009

    I am having this same problem. My Service Engine Soon light came on under normal driving and I dont hear or feel anything out of the ordinary.

  • Jose .A. Jimenez Mar 12, 2009

    have a 04 chevy blazer w/39,000 miles, service engine soon light came on, took it to Autozone for free check, code came up as po128. possibilities were #1- low coolant level, just had the system flushed and filled. #2- thermostat defective, never runs hot, avg. temp on gauge 190 - 200 degrees, I also checked firmness of top hose to double check t-stat, nice and pliable. #3- defective ECT sensor, I also tried the gas cap protocal and disconnect the positive from the battery. I figured I tried, everthing stated, I just couldn't find the ECT sensor, thought it would be next to the thermostat hub. Can you help me. thanks,Jose

  • Timothy May 23, 2013

    same here..i had codes for EVAP system..i had dealer replaced the one on the engine and just replaced the one at the tank..light stayed off for 2 days and came back on..when i had it checked at Advanced Auto, the guy said there was another code coming up that said thermostat..this is my next step to replace the stat unless someone has any other ideas..i love the car and hasnt given me any probs til now.

  • Timothy May 23, 2013

    i am having the same problem with my 04..I had it to the dealer and they said that the purge valve was the problem..They replaced it and 2 days later the light came back on. I took it to Advanced auto and theysaid it was a EVAP code. Also there was a thermostat code. Not running rough or stalling. Temp runs about 200. Next step is to replace the stat and see.. Unless someone has any other ideas.

  • Angela P
    Angela P Sep 07, 2014

    never anything wrong with the vehicle. And now they just go on and off all the time. I don;t know if this is helpful to you at all.


3 Answers

  • Level 3:

    An expert who has achieved level 3 by getting 1000 points


    An expert that got 10 achievements.


    An expert that got 5 achievements.

    Vice President:

    An expert whose answer got voted for 100 times.

  • Master
  • 333 Answers

1. Turn key to the "on" position but don't start car
2. Pull the PCM BAT and PCM IGN fuses in engine compartment
3. Wait approximately 5 minutes
4. Turn ignition off
5. Replace fuses
6. Start the car and the make sure the light has went off.
then check to see if your gas cap is on right. If this light comes on again then it is time for the dealer. If you can't find them fuses then just disconnect the battery for five minutes reconnect the battery and when you start the truck the light should be out. just let it idle for 2 minutes with no heater or radio on. and you set. I hope this helps you.

Posted on Dec 04, 2008

  • Level 1:

    An expert who has achieved level 1.

  • Contributor
  • 1 Answer

The Service Engine Soon Light has been mostly on lately, although it periodically goes off. Since we had a remote starter installed, we have had problems with the battery and the 04 Trailblazer sometimes needs a jump. Today, we had the back latch open and sure enough the vehicle needed a jump. The good news is ..the ses service engine soon light went out after that event. The advice to pull the fuses or disconnect the battery seems to have some merit Thank you ! I just hope it stays out !!

Posted on Nov 04, 2013

  • Ed Ward
    Ed Ward Nov 08, 2014

    you can get a code reader from the local parts store for about 60 bucks now.its been very handy on my trailblazer, since ive had to replace alot of small stuff causing the check eng light to come on.


  • Level 1:

    An expert who has achieved level 1.

  • Contributor
  • 1 Answer

Defroster is always blowing even tho i have heater knob on heater and have no heat on bottom by feet? could this be a vaccum hose?

Posted on Dec 27, 2008

1 Suggested Answer

  • 2 Answers

SOURCE: I have freestanding Series 8 dishwasher. Lately during the filling cycle water hammer is occurring. How can this be resolved

a 6ya expert can help you resolve that issue over the phone in a minute or two.
best thing about this new service is that you are never placed on hold and get to talk to real repairmen in the US.
the service is completely free and covers almost anything you can think of (from cars to computers, handyman, and even drones).
click here to download the app (for users in the US for now) and get all the help you need.

Posted on Jan 02, 2017

Add Your Answer

Uploading: 0%


Complete. Click "Add" to insert your video. Add



Related Questions:

1 Answer

Vehicle: 03 Chev Astro Cargo Van. Style: 2WD/RWD; 4.3 liter Engine Problem: Yesterday, 'Service Engine Soon' light came on, today Brake light and ABS Light came on

It could be many different of things, but I would check the charging system and battery first. I have had many under charging GM vehicles that all the dash warning lights would light up.

Jun 05, 2015 | 2003 Chevrolet Astro Cargo

1 Answer

1997 k1500. I started it today, negative temps, and I don't have 1st, or overdrive.

unplug the trailer first to see if it is something in it''s wiring.
not going into OD could just be that the load is too much to handle in OD.
speedo and tach I would start by checking fuses.
sounds like the problems are all related.

Jan 31, 2013 | 1997 Chevrolet K1500

1 Answer

Took my car (1994 Deville) to a GM auto repair Monday for an SES light on and they supposedly had the rear 02 sensor replaced and cleared the DTC as stated on the invoice. When I picked up the car...

even a dealer can make a simple mistake, But since you had the car done there I would take it back and ask them to re-clear the code, if there is a problem it will pop up again, since they guaranty their work,, if it does,, have them fix the problem

Sep 01, 2011 | 1994 Cadillac DeVille

1 Answer

Hi I have a Mini One, yesterday and tonight when I

hi it sounds like the engines electric cooling fan has automatically come on as the engine has got hot enough for it to be cooled down
you may have never noticed it before .
check your coolant level and your oil level to be on the safe side and keep an eye on the temperature gauge the fan should come on when the gauge goes past normal running teperature if its coming on a lot there may be a problem but its probably working as normal

Mar 10, 2010 | 2003 Mini Cooper

1 Answer

Similar Problem: Van bogs down when you step on the gas

2 simple causes for your symptoms would be water in the fuel tank (pour drygas into the tank to alleviate this problem) or a leak in the exhaust system. If both items don't apply, check for any vacuum leaks under the hood. You've isolated the problem to either vacuum leaks or a fuel problem. Hopefully, this will give you a general area to look and solve your problem. Best of luck.

Jun 22, 2009 | 2000 Chevrolet Venture

1 Answer

Car will no longer start!

Well, does this happen often, the engine failure? I'm not there in person, but I can lead you to an article that addresses what seems to be the cause of your car problem, and that is a malfunctioning connector between the electronic control unit and the distributor of the vehicle; here's the article link:

If, on the other hand--since putting gas into the gas tank was the last thing you did before you had a problem--consider the possibility you mistakenly read your gas tank gauge and unknowingly over-filled your gas tank, causing the problem you have been suffering right afterwards, as noted in this second diagnostic article: Good luck!

Jun 08, 2009 | 1996 Pontiac Sunfire

2 Answers

What is code 26

I'm sure the website cited will be of help. The infamous code 26 quad driver comes up pretty frequently on the Saturn Mailing List. One of the better technical explanations for pre-OBDII Saturns has been quoted several times. Here is the message, edited somewhat:
(credits to Ray Prill)

===== Quote on =====

> Yesterday, I saw my first Service Engine Soon light.
> I checked what code my car had stored, and it was #26.
> Code 26 (according to Haynes):
> Quad Driver output fault
> Possible cause: The PCM detects an improper voltage level on the circuit that
> is connected to the Quad Driver Module.
> Now, my questions are... What IS the Quad Driver Module, what does it do, and
> where is it?

Pretty vague, isn't it?

First of all, don't panic. Usually, this is not a serious
problem. Let me explain.

Code 26 is a *very common* SES indication to get with a Saturn that
has a few years on it. Most of the solutions, luckily, are not costly.
However, this may depend on the year of your car.

The "Quad Driver" is a device in the computer that "drives" electro-
mechanical devices in the car. Computers run with very little current
(milliamps or microamps) in their circuits. But the devices that
turn on your cooling fan, bulbs, or emissions relays may require
current in a higher range, say tenths of an amp.

Thus, the computer can't talk very well with such a high current
device. It needs help, and it gets in in the form of this Quad Driver
device. The computer sends a signal (very low amps) to the driver, and
it in turn then signals the electromechanical device to do whatever it
needs to do with a higher current which that device can use.

It sort of "drives" the device by remote control.

Code 26
OK, fine, that is the theory. So why the code 26? Well, in almost all
cases, the actual driver device does not fail. What fails is one of
the electro-mechanical devices attached to it. The way the SES light
works, it will come on when either one of the driven devices fails or
if the driver itself fails.

The good news is it is usually not the costly driver device. The bad
news is this is called a "QUAD" driver. That means it drives four
devices. Even worse, there are usually TWO quad drivers, so you have
a total of EIGHT devices to check for just this one SES light.

That's right, code 26 means that one of 8 devices (and a 9th, the driver
itself), could cause the problem. You have to check 8 different things.

Probable causes
I don't have my manual here, but I'll try to remember to post the
exact devices to check. The following is from memory, so bear with me.
Also, remember my car is a '91, so this may have changed somewhat in
following years.

The QD generally drives things like relays, solenoids and light bulbs.
There are a few things that are easy to check, like the bulbs and

The SES bulb and (I think) "HOT" bulb are driven by this device. You
should check that they both come on when you put the car to "on" before
starting. Of course, the SES must work, since it came on for you.

Then the A/C relay and Cooling fan relay are driven. For A/C, simply
check that your A/C works OK. The relay is pretty silent, unlike
some cars, so you can't always hear it click. Just make sure it works.
The cooling fan can be checked when you sucked out the code. Since you
know how to get the code, you should have noticed that the FAN comes
on for a while before getting the code out. (The bulbs also light.)
If the fan isn't coming on, check the relay. The Haynes manual probably
tells you exactly when the fan comes on during the procedure.
The relay is accessible in the under-hood fuse block.

After that, it gets tougher. You have to check some emissions solenoids.
From what I've read, the MOST COMMON cause of code 26 is either the
EGR solenoid or the canister purge solenoid. The EGR solenoid is
real easy to access. It sits right above the EGR valve and takes a minute
to disconnect on Sx2 models. The canister purge solenoid is a pain.
It is attached to the block on the firewall side. You have to take it
out blindly by putting your hand through a small "hole" between all the
hoses and wires.

I forgot what else is controlled by this device. I'll try to get
my manual tonight to look.

I had an SES light last spring. In my case, I guessed wrong.

I narrowed my SES last year down to the CPS or the EGRS, and incorrectly
deduced the CPS. What a pain to replace this. But I was wrong. That
wasted $20. My problem was the EGRS, and it was also a $20 part. Very
easy to replace.

I should mention that my symptoms were opposite of yours. Mine would
come on only while driving for a while, then go off when I stopped.
I should also mention that the CPS and EGRS are common causes of
code 26, and the irony is they are both Nippondenso parts, made in
Japan. How ironic!

Either way, if you take it for service, the Saturn diagnostic computer
should be able to discern between the two or any other device that
is causing this code. They can read more information than we can
by just pulsing out codes.

So, depending on your skill and your luck, you may or may not want to
try this. Like I said, most of the them are easy, thus even if Saturn
service does it, it usually is not costly.

==== Quote Off ====

And a followup:

==== Quote On ====
This is a follow up to yesterday's post about a "quad driver" fault.

Yesterday I mentioned the causes for a "code 26" fault with the
SES light. There I detailed the following causes:

1) SES light burned out
2) "HOT" light burned out
3) A/C relay
4) Coolant fan relay
5) EGR solenoid
6) Canister purge solenoid

I couldn't remember the other two causes. Remember, the "quad" in
the driver means it controls 4 outputs. Since there are 2 QDMs,
they control 8 outputs.

The other missing items to check are:

7) Speedometer output
8) Upshift/Shift to D2 bulb

Hope this helps. As you can see, most items are easy to
check except for the solenoids. These can be checked by
measuring their resistance.

Apr 21, 2009 | 1995 Saturn Sl

1 Answer

2003 Saturn L300 indicator lights stay on: ABS, SES...etc

first problem, went to autozone. the guy that looked at your car was making pizzas last week. they pull codes and sell you every part you will buy. take the car to the saturn dealer and replace the bcm.

Mar 02, 2009 | 2006 Saturn L300

1 Answer

I have a 98 intrique . as i was picking up speed my car cugged and my rpm's bounced high then down and then after trying to drive through it i was able to hit about 65 mph but still noticed the hesitation...

yes. your exhoust problem has likely caused a result,the oxygen sensors in the exhoust system are probably now bad.these sensors will couse the ses light to stay on.

Dec 02, 2008 | 1998 Oldsmobile Intrigue

1 Answer


Good Day,

If I were you I would clear all the codes, then drive around until your SES comes on. Instead of shorting pins take it to an autozone(they do it for free) or shop that has an OBD2 reader, they can read your code and tell you exactly what sensors are causing this problem. I can cross refrence codes for you aswell if they only provide you with the code number.

hope this helps again

Jul 06, 2008 | 2005 Chevrolet Equinox

Not finding what you are looking for?
2004 Chevrolet TrailBlazer Logo

6,785 people viewed this question

Ask a Question

Usually answered in minutes!

Top Chevrolet Experts


Level 3 Expert

64052 Answers

Colin Stickland
Colin Stickland

Level 3 Expert

21990 Answers

Jeff Turcotte
Jeff Turcotte

Level 3 Expert

6812 Answers

Are you a Chevrolet Expert? Answer questions, earn points and help others

Answer questions

Manuals & User Guides