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Discussion Starter #1
Hey guys I got a 07 ss trailblazer I been working on for 3 months. The problem is the u0100 no communication with pcm. I got another pcm no luck the brought a new pcm and new bcm. Still now luck it's getting power and ground to pcm. But I noticed don't have a 5volt reference. Also I noticed that my battery gauge sits and moves back and forth between 6 volts and 12 volts.
 

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2002 chevy trailblazer_lt
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Is your scanner reading these codes from the DLC? Or is the whole network down? If your problem is in wiring somewhere then replacing modules isn't going to change anything. Was the 5 volt ref dead with all the PCMs you've had in there?
 

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Discussion Starter #4
I tried the 5 volt reference through the map sensor and mass air flow sensor and electric throttle under the dash
 

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So there is no communication happening at all, including no scantool communications then?

In that case I would pull the comb from the data splice pack at the left side of the dash and try connecting just the minimum modules of PCM & BCM to see if you can get comms up. If that works you then add modules back, one at a time toll you find the one that is crashing the comm link.

Watching this might help...

 

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Discussion Starter #6
Is it possible for me to leave u my number on Facebook messenger or u n box me yours so I can have specific details. I'm trying to get this thing running before the summer is over lol.
 

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Is it possible for me to leave u my number on Facebook messenger or u n box me yours so I can have specific details. I'm trying to get this thing running before the summer is over lol.
I believe thse things are better addressed online like this for a couple reasons. One is that I do better with written records of details because I forget things!! I need to refer back to the specifics frequently. Secondly, having it worked out online helps others who may find themselves in similar situations. And lastly, I get sh** wrong all the time so having in a group is helpful where others can straighten me out!!
 

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Discussion Starter #10
Yes I pull it the wiring diagram and check all of the 12 volt power supplies and I have the 6.0 ss3
 

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I tried the 5 volt reference through the map sensor and mass air flow sensor and electric throttle under the dash

Not having any 5 volt reference signals would suggest a bad ECM if you have already confirmed 12 volt power at ECM connector 1 pin 18 (hot in acc, run or start), pin 19 (hot in run or start) and pin 20 (hot at all times). Either that or there are some short circuits to ground pulling the 5 volt circuits down.

Oh, and the MAF doesn't use a 5 volt circuit by my diagram. It has a 12 volt, a ground, and a signal back to the ECM. But the accelerator pedal and MAP should have had a 5 VDC reference.
 

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What is the history of the vehicle? Was it running and died on you or did you buy it this way?
 

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I would probably bet on a short circuit. If I leave the battery connected with key on battery gauge movies from 6-14 volts back and forth. And after about 20 minutes the battery is died. My plan was the use the video u sent and check each circuit and see if one has a bad module.
 

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I think it unlikely a short in a 5 volt circuit will run a battery dead in that short time. Possible I guess but I'm suspecting multiple issues here. Maybe pull fuses for all unnecessary items to see if one of them is pulling down the battery?

And what's the history here? Is this a new-to-you vehicle?
 

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battery connected with key on battery gauge movies from 6-14 volts back and forth. And after about 20 minutes the battery is died.

I would experiment. Put a meter on the battery to read voltage. Does the battery voltage drop and go dead with the key off? .... No? Then what does the meter read when you turn the key just enough to bring on the battery indicator on the dashboard, not so far as the accesory position, just far enough to bring on the little red battery picture in the dash?

Voltage drop on the meter when you turn to the accesory position? Keep going slowly with the key, looking for when the battery starts that cycling low to high to low and so on. The key actually brings circuits on in stages and maybe by turning it slowly and observing the voltages you might be able to isolate what circuit has the big drain on it.
 

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Discussion Starter #16
Yes I brought the truck at a police auction. It was a stolen recovery. I had to replace the steering column and wheels everything else was still their. But I have no idea on the history
 

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had to replace the steering column

Well that right there opens up a significant possibility of a shorted or misconnected wire...

I would rate the battery drain/short circuit as 1st priority, the 5-volt and communications after that.
Something that pulls the battery voltage down that low is going to kill the communications as well as disrupt any 5 volt regulated power supply circuitry.
 

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So here is something to question. If the reader has no communication with the ECM/PCM..... Where is it reading that code from?? I am thinking that reader throws that code out to the display whenever it can't establish communications with the PCM/ECM
 
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