NEED HELP 2005 Trailblazer EXT V8, no crank, no start, no locks, now front windows, ABS and airbag lights on.

ZX2Fast

Original poster
Member
May 21, 2019
5
Anderson, Indiana
I sent my PCM out to East Coast Superchargers for a mail-order tune. I got it back, installed it, and everything was fine. It had about 3 hours of idle time on it and maybe 30 minutes of driving. I drove it to town one day and noticed all my gauges except the speedometer and tach weren't working and my ABS and airbag light were on as well as the 'check gauges' light. It was still running. Came back and it starts but same issue, notice my front windows won't go up or down, my power locks don't work, heated seats didn't work, and my radio was off, no power to it. Got it home, turned it off, it wouldn't restart. Tried leaving the battery cable off for a day and still same issue. Sent PCM back to have it checked, checked out okay. I didn't notice I had the key in ACC when I hooked the battery back up, I had radio power and windows, seemed like everything was okay. I started it and pulled it out, made it 20 feet before I got the same problems again. It would restart multiple times even with the issues, but on the 7th-6th attempt, no crank no start. I could get it too act normal if I took the cable off and reconnected it, even my radio would come on but the volume button turned it down even if I pushed 'UP' on the steering wheel controls. It has an aftermarket stereo with a PAC interface. I unhooked the battery and removed the interface, same problem. I cleaned the grounds under the hood that I could find, one on the driver firewall, one forward of that on the fender, and one on the passenger fender, same issue. The big fuse is good as well. Removed the BCM (under the 2nd row seat) and checked the ribbon cable for open circuits, it was good. Looked in the module and no obvious electrical shorts. Other BCM functions seem too work, like the interior lights. I even replaced the ignition switch and that didn't fix it. When I turn the key to 'run' the security light comes on and goes off like it should. If I jump the starter with the key in 'run', it starts and runs for a few seconds, the way they do when security disables them.

I have found a BCM with the same p/n and the 'red' sticker just like mine, but I didn't want too try it unless I checked here first. I have heard some people having this issue with performance tuning, but they said it checked out on their end. I can access the PCM with a scan tool, can't see the BCM, ABS module, airbag module, or the transmission module (but it will shift when it is running) with the scan tool.
 

xavierny25

Member
Mar 16, 2014
6,323
Staten Island, N.Y
Have a look at the passenger side footwell for a ground pack just under the carpet close to the center console. Clean that bad boy up its known to cause all types of gremlins.

What brand ignition switch did you use? Its acdelco or nothing on these trucks.

I've haven't heard of any ill effects from a tune on these trucks but most guys here either used @limequat or pcm of nc. Can you post up the tune sheet for the tuners here to have a look at.
 

Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
Check that all your fuses, underhood and under seat, are all good with a test light on the fuse contact points, not visually. Test for proper power at the ignition switch to be sure all circuits are being powered.

Never heard of anyone having issues with a tuned PCM except having to do a security relearn if it's not the original PCM. And replacing the BCM won't help you as the VATS will throw fits not seeing the proper resistance from the key sensor. It would need to be reprogrammed with a Tech 2 or at a dealer and it has to be done in the truck since the BCM is the master of all.

Download the manuals for the schematics (link in my signature) to see which circuits maybe affected and for the ignition switch wiring and power.
 
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ZX2Fast

Original poster
Member
May 21, 2019
5
Anderson, Indiana
Check that all your fuses, underhood and under seat, are all good with a test light on the fuse contact points, not visually. Test for proper power at the ignition switch to be sure all circuits are being powered.

Never heard of anyone having issues with a tuned PCM except having to do a security relearn if it's not the original PCM. And replacing the BCM won't help you as the VATS will throw fits not seeing the proper resistance from the key sensor. It would need to be reprogrammed with a Tech 2 or at a dealer and it has to be done in the truck since the BCM is the master of all.

Download the manuals for the schematics (link in my signature) to see which circuits maybe affected and for the ignition switch wiring and power.


I did use a volt/ohm meter to check each fuse for continuity. They all tested good. I used a switch from Auto Zone, but I have installed several remote starters and checked the output of each wire on the old and new switch, they tested good. I ended up reinstalling the old switch since they both behaved the same.

I don't have a tune sheet. I talked to the tech that does the programs (he also did my Corvette) and he says the only time he has seen an issue like this is when they flash the PCM in the vehicle and the BCM doesn't wake up when they restart.

I have seen several relearn videos for passlock 2 about leaving the key on for 10 minutes (after turn to crank) and do that 3 times, does that not work?

I have downloaded the manuals and will try going through them later tonight, I just cleaned the ground next to the passenger side console since it grounds a lot of what I am having issues with.

I do appreciate your help.

I have a good deal of experience installing electrical in vehicles and troubleshooting. I know a ground feedback can cause all sorts of issues in these CANBUS systems. But my gut is telling me my BCM is toast.
 

gmcman

Member
Dec 12, 2011
4,656
Was the PCM you sent out the exact same one that was returned?

Not saying you cannot use a different PCM, don't remember what the compatibility is with gear ratios, but if it was working fine on the stock PCM, now it's acting up....I would retrace your steps with what you disconnected and ensure all the positive leads at the fuse box are secure. Main reason is you know your PCM was fine before, and only to ensure you didnt receive one that could have an issue inside.

I would pull the harness for the PCM and make sure all the pins look to be uniform in length and/or not bent. Unlikely but worth a look.


Did you ever have any of these issues before the PCM upgrade?
 

Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
Looking at your symptoms, I wonder if it could be something screwing up the data bus?
 

ZX2Fast

Original poster
Member
May 21, 2019
5
Anderson, Indiana
Was the PCM you sent out the exact same one that was returned?

Not saying you cannot use a different PCM, don't remember what the compatibility is with gear ratios, but if it was working fine on the stock PCM, now it's acting up....I would retrace your steps with what you disconnected and ensure all the positive leads at the fuse box are secure. Main reason is you know your PCM was fine before, and only to ensure you didnt receive one that could have an issue inside.

I would pull the harness for the PCM and make sure all the pins look to be uniform in length and/or not bent. Unlikely but worth a look.


Did you ever have any of these issues before the PCM upgrade?

It is the same, it had the same tape, same paper over the ports, and even in the same box.
I had several hours of idle time (was cleaning the inside, carpet was dirty and I have a Bissell) but only very little drive time. I checked the pins before I installed it this second time, they are straight. I did not have any issues before the PCM upgrade. If I can't get it too work, I will have the PCM flashed back too stock.

Looking at your symptoms, I wonder if it could be something screwing up the data bus?

I have wondered the same. I unhooked all the aftermarket stuff (stereo, rear power station, etc.) that I installed and still the same result. I have even pulled the connectors from the Motorola box (for the Onstar) and the sat radio, same problems.
 

Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
I have wondered the same. I unhooked all the aftermarket stuff (stereo, rear power station, etc.) that I installed and still the same result. I have even pulled the connectors from the Motorola box (for the Onstar) and the sat radio, same problems.

You might have to go deeper and pull the comb from the data bus main connector. It's a taped up wide black connector with multiple wires going in one side but none going out the other, located under the driver side dash. Once you remove the tape, you see the metal comb that connects them all together. Using the schematics, jumper only the PCM, BCM and OBD diagnostic connector and see if it starts. You will get all lights on in the dash.

There have been instances of an individual module, like a door module, that totally buggered up the data bus and prevented stuff from working. Are you able to communicate with the PCM to try and pull codes?
 

budwich

Member
Jun 16, 2013
2,027
kanata
I wouldn't going "crazy" disturbing a lot of things IF the only thing that you had previously "touched" was the PCM... it is unlikely that things "broke everywhere".

You need to step back.... restate exactly what the current status of the vehicle is as the thread has wondered a bit with you trying different things. So does the truck start at all currently? IF NOT, then that's good, it gives a place to begin as the start circuit / system is compact and allows to look at just a few things. IF it does start, describe what you see / how it runs. IF there is lots of things "bad", then you are going down a longer road of investigation, but again try not disturb things, just do checks at this stage. My first guess is you blew a fuse somewhere.
 

limequat

Member
Dec 8, 2011
520
Hmm, sounds like a mess. A few clues:
* A tune would not do this. A loose PCM connector, maybe.
* Speedo, tach are the only gauges NOT on the bus.
* Start goes like this: BCM reads key, if OK, sends serial message to PCM to start. PCM pulls in relay.
 
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ZX2Fast

Original poster
Member
May 21, 2019
5
Anderson, Indiana
So I figured it out, you won't believe it. The factory DVD player did it. I was unhooking one thing at a time and thought, what the hell, unhook the DVD player. I had the key turned on and when I hit the power button for the DVD player, the stereo and dash came back on. I pulled the player down and checked it over, the board with the inputs and parent button smelled burnt, replaced that and it has only had the dash fail once and tapping the player fixed that. Of all things...
 

mrrsm

Lifetime VIP Donor
Supporting Donor
Member
Oct 22, 2015
7,642
Tampa Bay Area
'Of ALL Things' is RIGHT... GM's Class 2 Network Data-Bus functions as a Single Wire System operating at a Minimum-Maximum of 0-7 VDC for Signalling and all of the Module Network Segments eventually come together under the Dash Splice Pack perfectly described by @Mooseman. There has been an instance where the Entire SUV "Net" was brought down by a Kid slipping coins inside of the Radio-DVD Player Slot and Shorting the "Net:" directly to 12 VDC. So... Very Nicely Done on sorting this Nightmare OUT! :>)

Just in Case you have to Keep Diagnosing things...This is a Diagram of the GM Trailblazer Class 2 Network:

COMPUTERDATALINESYSTEM.jpeg
 

Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
Not the first time that a single module or the radio would screw up the data bus. Good job and thanks for updating this thread.

:thumbsup:
 

ZX2Fast

Original poster
Member
May 21, 2019
5
Anderson, Indiana
I sold it a few days ago because I found a deal on a 2010 Volvo XC90 V8 I just couldn't pass up. Thank you all for your help and I hope this thread can help others in the future.
 

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