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2004 chevy trailblazer_lt
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allen410 - Welcome to the Forum!

Also, allen410 - accept it, you were led astray by the youtube videos in so many different ways. Now, if you really want assistance in helping you figure out what is wrong with your TrailBlazer, then you are going to first, admit to yourself that you were given erroneous information on youtube. Second, you are going to have to learn how to diagnose problems on modern vehicles, and third, you are going to need to purchase a couple of necessary tools (which are actually quite inexpensive compared to the cost of unnecessarily replacing one or two functioning properly parts). Third, you are going to have to put up with our questions because you are there, we are not, and we cannot magically see your TrailBlazer, and what you are doing to it, so we tend to ask some very specific questions in order to keep from sending you down the wrong diagnostics branch, and we might even ask for a picture or two.

OK, now for the required tools. If you do not already own them, you will need a decent Digital Multimeter (DMM) and a decent code reader/live data scanner. If you have an android device, then this combination of a Bluetooth OBDII dongle and Torque Pro app is hard to beat, and it costs less than $25.00 ($5.00 for the Torque Pro app, and anywhere from $12 - $20 for the dongle on Amazon). Here is the link to the Bluetooth Dongle (which currently sells for $13.99):


Now here is why you should never, ever disconnect the battery for routine diagnostics:

DO NOT DISCONNECT THE BATTERY - REMOVE THE APPROPRIATE FUSE(S). Why? Because when you reconnect the battery, the HVAC actuators inside of the dash are commanded to run a recalibration procedure which stresses the old brittle plastic gears inside the actuators and the brittle plastic gears break and leaves you unable to control where the air comes out, or control the temperature of the air, etc. Replacing at least one of them literally requires the removal of the entire dash! So, if you ever need to actually disconnect the battery, such as in the case of needing to install a new battery, be sure and use some kind of Keep Memory Alive device to avoid the HVAC actuator recalibration routine.

Now a couple of things.

One, when you do a parasitic draw test, you have to wait about 30 minutes before you begin reading the amount of current in Amperes (or milliamperes) being drawn from the battery. Why? Because all of the computer modules do not go to sleep the moment you shut the engine off.

Two, to measure parasitic draw, you put the multimeter into current mode and then you put the DMM in series with a battery cable. You do not measure current or voltage going from a vehicle ground to the battery unless you are doing a voltage drop test or are looking to create some fireworks with an exploding battery (when the DMM is in current mode). When you do this, remember to hook up a KAM device in parallel with the DMM until all the modules go to sleep.

So now, starting at the beginning, how may we help you (and please do not forget any OBDII codes you are aware of)?
 

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Premium Member
2004 chevy trailblazer_lt
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OK, now we are on to something! The first thing you have to realize about this vehicle is that everything is controlled by a computer module of one kind or another. The Engine Control Module (or Powertrain Control Module) (ECMor PCM) covers the engine and partially the transmission. Then there is the Body Control Module (BCM) which controls the interior and exterior lights, the door open chime, the seat belt chime, the radio, the HVAC, etc. (it's a long list). Then there is the liftgate module often referred to as the read BCM.

Now, in order for the TrailBlazer to run properly, it must have good clean voltage in the range of 12.2 to 14.0 VDC (give or take a little). AC ripple out of the alternator must be 20 mV or less otherwise it will mess with the electronics. Electrical connectors must be fully seated and tight and clean. Grounds are super important and they must also be clean and tight. Battery cables need to be free of the green grunge disease, and unless you really want problems, please heed the following:

(I know I put this in earlier, but it needs to be stated over and over)
DO NOT DISCONNECT THE BATTERY - REMOVE THE APPROPRIATE FUSE(S). Why? Because when you reconnect the battery, the HVAC actuators inside of the dash are commanded to run a recalibration procedure which stresses the old brittle plastic gears inside the actuators and the brittle plastic gears break and leaves you unable to control where the air comes out, or control the temperature of the air, etc. Replacing at least one of them literally requires the removal of the entire dash! So, if you ever need to actually disconnect the battery, such as in the case of needing to install a new battery, be sure and use some kind of Keep Memory Alive device to avoid the HVAC actuator recalibration routine.

Now, I am not a pro, but I've been repairing cars since the mid 1970s and about the only thing I am hesitant to mess with is an automatic transmission. I'll rebuild Rochester Quadrajets all day long, but other than doing an AT fluid and filter change, I don't mess with transmissions.

Now a couple of random goodies before I forget. There is an important ground in the passenger compartment and it's located under the carpet immediately to the right of the gas pedal where the foot rests. For some reason, it loosens up and corrodes and when it does, it causes havoc. The alternator is controlled by the ECM. Weird unexplainable electrical gremlins such as the windows going down on their own, the radio changing stations by itself, the clock in the radio resetting randomly, dash lights misbehaving, etc., point to an ignition switch going bad. With the ignition switches, it is not a matter of if it will go bad, it's a matter of when it will go bad.

Well, since rodents have been having a feast on your TrailBlazer, I fear you are going to have to endure some nightmarish things for awhile as you track various things down. Now, if you have a high parasitic current drain, the first thing I would do is to pull the fuse for the OnStar module. I'm sorry but I don't know which fuse that is, but I do know you can download a copy of the owners manual from the GM website.

I do have a copy of the factory service manual in pdf form and it is broken up into sections. If you want one, you can download it from the GMTNation website. Here is the direct link: Need service manuals? Get them here!

Make sure your alternator is putting out adequate voltage and current, get a load test on the battery just to make sure it does not have a bad cell.

Good Luck and please don't be shy!
 

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Premium Member
2004 chevy trailblazer_lt
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2,756 Posts
Well, it could be one of two other things. One, it could be that the ignition switch is bad. Two, it could be that the instrument cluster is going bad.

On this series of vehicles, the ignition switch is known to go bad. The question is not if it will go bad, but when will it go bad. Many of us carry a spare ignition switch for when the time comes. Here is a nice write up on how to replace the ignition switch:


Diagnosis of a bad ignition switch is by exclusion - ruling everything else out, or by the weirdness factor - why is it my dash lights only work on the third Thursday after a full moon and my radio thinks it has become a scanner whenever I hicup.

One other cause - a light bulb on the instrument cluster is brighter than it should be and it is kind of like "bleed over", but this only happens when the instrument panel is illuminated.

Here is some interesting reading:

 

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Premium Member
2004 chevy trailblazer_lt
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I'll keep my toes crossed for you!
 
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