2004 Trailblazer fixing an issue caused by an idiot

Let me start by saying the Idiot was me.... now moving on.
I am working on a 2004 Chevy Trailblazer 4.2L V6 RWD.
Now to the issue...
Instead of going into how I was an idiot and caused this issue... the problem was/is The primary wiring harness that runs between the Front splice pack in the dash SP205 along with all the other wiring in the front of the vehicle and the BCM and rear splice pack SP306 and rear distribution block all located under the driver side back seat. The harness was cut approximately 10 inches from the Automatic restraint module located under the center console basically right as the harness passes the console headed toward the back. reconstruction of the harness was fairly easy until I found 3 yellow wires, 2 Light blue wires, and 2 Light Green wires. when the wires were cut the following systems were effected: PAsskey stopped working, caused a No crank, no start situation, back speakers where affected, that is all that was noticeable...

After working out the Yellow wires, and connecting the blue ones with a best guess, as well as the green wires, the following is present... The blazer starts, runs, everything works power windows, radio(aftermarket), seats, wipers ect.. 0 Computer errors from the code reader/scanner tool I have.

I have the following issues: Security indicator is always on, as well as the Airbag light, when connecting to a Advanced scan tool (one from orileys auto parts) it shows no communication with the front hub speed sensors and BCM Serial data is shorted to ground.

Note with both green wires disconnected,,everything still starts/runs coming from the BCM toward the front one wire is hot all the time, on the front side of the cut one is grounded the other is an open circuit.

I have traced the serial data wire down to one of the 2 LT Green wires- if i connect it to the light green wire that is grounded I get the ground error, If i connect it to the wire that tests as an open circuit (via scope on a rope) the blazer will no longer start and it is back to the 30 min passkey relearn... after the relearn when you try to start the blazer it faults back to security relearn again. open the circuit and all works again. I have a feeling one of the light blue wires is connected incorrectly and causes the security to fault when class 2 serial coms is restored when connecting the green wires...

My question is this, is there some documentation some where that us non mechanics cant find that shows the actual pinout of the BCM/rear Distribution block connector and the splice connectors/ other connectors so I can trace the wires out.?

I have the full wiring diagram of the 2004 Trailblazer and it even has color codes and pin locations on plugs but does not offer any information on the orientation of the plugs so I can find the correct wires...

Quick edit ... I am trying to avoid removing all of the interior again. so I would prefer to do end point tests

Hey Nemesis! Any idiocy aside, I'd love to help you figure this one out.

I gotta say, though, not having a full function scanner available will make this difficult. Nothing against your O'Reilly's scanner, but being able to query all modules on the network for codes would give us a better overall picture of the issue.

Anyway, I've been looking at the wiring diagrams, trying to determine which light blue and light green wires you've working with. It gets complicated because there are anti-theft options. The 'Immobilizer' option has an independent Theft Deterrent Control Module which. The 'w/o Immobilizer' option just uses the BCM. Both options talk on the Class 2 network, and both have discreet communication lines with the PCM.



I believe at least one of the light green wires you're working with is this one:



Where the other light green wire is coming from/going to, I have no idea. :blush: But I think it makes sense to first identify which wire is coming from SP205, and which one is coming from the BCM. Once we know that, you can connect them permanently, or label them as needed for future reference.

My question is this, is there some documentation some where that us non mechanics cant find that shows the actual pinout of the BCM/rear Distribution block connector and the splice connectors/ other connectors so I can trace the wires out.?

Usually, yes, depending on the Y/M/M. I can't say if that kind of info exists for your trailblazer or not, but GM is usually very good about making that kind of info available. Mitchell DIY would be an affordable option.

Pin-outs would be nice to have, but I'm not sure you need one yet. We can likely determine for certain which light green wire is the Class 2 network, with some ohm checks at SP205 and the BCM. SP205 won't be hard - remove the comb and find the only light green wire present. Connect your DVOM there, and use the other end to check both of your light green wires. One should have continuity.

The one at the BCM will be tougher. The light green wire we want is in Connector 1, pin B1. Three connectors at the BCM - grey, tan and black. Grey is C1. B in B1 usually means the second row of pins. The wire color sequence you're looking for is as follows (pieced together from other diagrams):

B1 Light Green (The one we want)
B2 Black
B3 Light Green
B4 Grey/Black

I can't imagine that exact wire sequence would exist anywhere else in C1, so it should be unmistakable when you find it. Connect the DVOM to B1 and probe your cut light green wires to find which one of those is the right one. Connect your wire that you ID'd from SP205 with the one from the BCM.

Did that make sense? :silly: Mostly, I'd like to nail down this circuit so we can go on to figure out the others. This seemed like the easiest to trace.