GMLAN circuits 2500 and 2501

JAMESB2019

MEMBER
2006 PONTIAC G6
3.9L
V6
2WD
AUTOMATIC
160,000 MILES

In the diagrams attached, can DLC pins 6 and 14 be tested for continuity to TCM pins 6, 7, 37 and 38 as well as to ECM C3 33 and C3 53 and BCM C2 1, 2, 19 and 20 while the battery and modules disconnected? Are there direct wiring connections between all of them with respect to circuits 2500 and 2501? Or are the connections fused or require voltage? I am trying to test 2500 and 2501 GMLAN +/- High Speed circuits from the various modules to the DLC. I know this is a bit asking too much of you but can you help? I attached some images I have summed up myself from various sources and used to test, but somehow I am not getting reliable connections. For example the attached electrical diagram (the one that is original- the last one I uploaded on here) shows symbols and connections between the TCM pins and the ECM I am having difficulty applying. The same thing is happening when I test the DLC to the TCM.

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3 Replies

KASEKENNY

MECHANIC
18,907 POSTS

This communication network is slightly different then regular vehicle wiring. So you actually cannot do continuity or resistance checks from the DLC to actual module. First the DLC communicates directly with the BCM but then the BCM communicates with each module through a vehicle communication interface module. So there is no direct circuit connection from the DLC to each module.

Here is a guide that talks about these types of networks in more detail:

https://www.2carpros.com/articles/can-scan-controller-area-network-easy

Also, take a look at the wiring diagram below as it is a little more clear on the what this communicates. You will see the DLC in the upper left side and that communicates with the BCM. Then you can follow the tan wires down to the VCIM which then communicates with each module in series.

Is there a reason that you need to test this network? If there is an issue with it you will have all sorts of codes that are either loss of communication or network performance codes. If you do not have any of these then the network itself is okay.

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Wednesday, July 7th, 2021 AT 11:40 AM

JAMESB2019

MEMBER
42 POSTS

Hi,

Okay, so yes the main reason why I ended up having to test the GMLANS was not knowing the answer to the question you already answered for me (thanks a bunch). And the reason why I had that question was because I had to splice a new TCM connector and its wiring and a new C100 AT wiring and connector. That was done because of an ISS 717 code that wouldn't go away even after I myself replaced the ISS and replaced the TCM and had it reprogrammed. Once I spliced the new connectors and wiring and started up the car, the transmission went into limp mode due to ignition 1 voltage circuit fault as well as communication with BCM lost message. So, I ended up undoing the splices I had made to check for integrity and guess what I found: The pink ignition 1 voltage wire was severed. The previous owner had used the pink wire to bunch up the remaining wires and tied it up like a zip tie. So, when I was doing the splicing I had to cut a portion of that pink wire which made it shorter than normal and after I was done splicing and encasing the wires in their new flex tubing, it pulled away from its sister wire. Actually, I just got done working on all the circuits and all is well. I ended up using a combination of methods to be sure all the circuits were connected correctly: the BCM showed continuity to the DLC. TCM pins 38 (2500) and 37 (2501) showed continuity to the C3 53 and C3 33 (ECM), respectively and the EBCM B12 and B9 showed continuity to TCM pins 6 and 7 (2501 and 2500). And as you explained, not all GMLAN circuits were going to show continuity. I had enough clues to get the job done though. Now my sister (who I bought this G6 GTP for) is giving me that look: "is the ISS fixed?" I said to myself I forgot what I started fighting for! I didn't see any OBDII codes though, so I said "I think so." Whatever happens I am ready for the rest if needs be (the rest? I mean opening up the side case again and see if there is any debris in the connector, see if the Reluctor Ring is okay, the solenoids or the valve body have any issues). Of course, I wouldn't dare reminding her of the possibilities! So, let's hope this was a wiring issue as it appears to me to be so.

James

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Wednesday, July 7th, 2021 AT 7:39 PM

KASEKENNY

MECHANIC
18,907 POSTS

Totally understand. It does sound like that is what it was. If it were debris then it would likely continue to acting up once it starts.

I would feel confident about this one. Thanks for the update and using 2CarPros.

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Thursday, July 8th, 2021 AT 7:42 PM