Question about 2004 Chevrolet TrailBlazer

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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,

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  • 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.



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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

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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.


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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

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