Module confusion and issues on my 2008 LMM

[JoshH]

Not sure how? The X3 pin 19 is the low speed serial data enable buss. Dean

I'm just telling you what I see in the diagram I have access to. The pinouts for each connector are attached below. You can see they have the same circuit number and description there.

This is what I see in the prints. J1pin 1 which goes directly to the splice saver. Am I missing something? Dean

Diagrams are sometimes dependent on vehicle configuration. Obviously your vehicle isn't configured to have the VCIM spliced into pin C of that splice pack, but since my diagram shows an alternate method, perhaps that is how yours is wired. That's why I suggested you perform a continuity check on the circuit to verify. I have attached the wiring diagram below. You will notice it shows both configurations in my diagram. Obviously only one is correct.

 

[Dean E]

I'm just telling you what I see in the diagram I have access to. The pinouts for each connector are attached below. You can see they have the same circuit number and description there.



Diagrams are sometimes dependent on vehicle configuration. Obviously your vehicle isn't configured to have the VCIM spliced into pin C of that splice pack, but since my diagram shows an alternate method, perhaps that is how yours is wired. That's why I suggested you perform a continuity check on the circuit to verify. I have attached the wiring diagram below. You will notice it shows both configurations in my diagram. Obviously only one is correct.

Thank you! I was wondering what I might have been missing from the VICM and this could be it. Needless to say GM did not do a very good job of keeping this all within one or two splice packs. This low speed databus still goes out everywhere in this system. This would be so easy to trace down if the problem was hard failed. It is a big reason I'm not wasting money going to service shops on it. Most would put 2 or 3 hours of TS in it and throw a module at it. Dean

 

[Dean E]

I'm just telling you what I see in the diagram I have access to. The pinouts for each connector are attached below. You can see they have the same circuit number and description there.



Diagrams are sometimes dependent on vehicle configuration. Obviously your vehicle isn't configured to have the VCIM spliced into pin C of that splice pack, but since my diagram shows an alternate method, perhaps that is how yours is wired. That's why I suggested you perform a continuity check on the circuit to verify. I have attached the wiring diagram below. You will notice it shows both configurations in my diagram. Obviously only one is correct.

Well, everyone I have not communicated much on this issue for a bit simply because it has not occured since I wired this up like a lab experiment. With diesel prices the way they are honestly the truck has not been used much. I did make a run to St Louis and back to move my son there and about once a week to work and back. Like I stated before the issue would clear wiggling the wires to the VICM but unplugging the X1 and X2 connectors would not clear the issue. When I wired this up for testing I did put a tie wrap on the VICM wiring harness to route my high and low to my oscilloscope. I now think this cleared (or at least isolated) my issue. Today I unwrapped the two electrical connectors going to the VICM to see if there was anything obvious. The connector that does not have the single wire GMLAN low speed wire on (X2) it did have some piss poor shielding grounds. What it looks like is an aluminum wrapped shielding. One has a single wire and the other has two wires. These are taped to a bare wire that runs to the other X2 connector. Definitely not aircraft wiring quality! Other than that everything looks good. I separated the shielding stuff from the rest of the wiring and will drive the truck a bit more to see if anything pops up. Any detailed wiring to the VICM on this would be greatly appreciated. The wiring manual I got from @Ron Nielson does not have much on this or at least I can't find it.

 

[Dean E]

Here is a look at the wiring

 

[Dean E]

Well I hope this is the final nail in the coffin on this matter. My problem is completely gone. Although I did not find a smoking gun my problem definitely was in the shielding for the antenna coax. Taking an issue like this to a dealer would have cost thousands and probably not correct the issue since it was so intermittent. The one thing worth its weight in gold is the Uscope unit. This small single channel oscilloscope is a wonderful tool and worth every penny. It is surprising to see that when the buss is corrupted it takes a few seconds before you see a reaction in the truck. Having the Uscope connected to the GMLAN low speed serial buss while driving definitely helped me zero in on my problem. You can see the exact moment the buss goes down (high or low) and the exact moment it comes back. On my truck the buss was going low meaning it was either a module or wiring that was shorting to ground. If you have it were the buss fails high (constant 6 to 7 VDC) on the scope then your issue is very likely a module. I was lucky enough to have the VICM in close proximity to the driver seat so I could play with the wires when the serial buss acted up. It was most certainly a learning experience but one I am glad to have behind me. I hope others will be able to find all this and use it to their advantage. Thanks for all the help, Dean

Source: https://youtu.be/aazmvhgZpy8?list=PL-Rl7bcueUT1YdOGGMXw3LgNxLFGi1EZt

 

[1FastBrick]

Dean, Thanks for taking the time to come back and post an update!
I am sure some one else will find this useful information.

 

[Chevy1925]

Well I hope this is the final nail in the coffin on this matter. My problem is completely gone. Although I did not find a smoking gun my problem definitely was in the shielding for the antenna coax. Taking an issue like this to a dealer would have cost thousands and probably not correct the issue since it was so intermittent. The one thing worth its weight in gold is the Uscope unit. This small single channel oscilloscope is a wonderful tool and worth every penny. It is surprising to see that when the buss is corrupted it takes a few seconds before you see a reaction in the truck. Having the Uscope connected to the GMLAN low speed serial buss while driving definitely helped me zero in on my problem. You can see the exact moment the buss goes down (high or low) and the exact moment it comes back. On my truck the buss was going low meaning it was either a module or wiring that was shorting to ground. If you have it were the buss fails high (constant 6 to 7 VDC) on the scope then your issue is very likely a module. I was lucky enough to have the VICM in close proximity to the driver seat so I could play with the wires when the serial buss acted up. It was most certainly a learning experience but one I am glad to have behind me. I hope others will be able to find all this and use it to their advantage. Thanks for all the help, Dean

Source: https://youtu.be/aazmvhgZpy8?list=PL-Rl7bcueUT1YdOGGMXw3LgNxLFGi1EZt

aint a hell of a feeling when you finally figure something like that out! Awesome to hear

 

[Dean E]

aint a hell of a feeling when you finally figure something like that out! Awesome to hear

Yeah, nothing is more frustrating that an intermittent issue like that. I have seen quite a few videos on Youtube where people just gave up and just traded the truck in at the dealer. Problem for me is I love my 08 LMM. Got 200k on the odometer and the old girl still looks pristine. If something happened to it I doubt I would get another diesel. The DEF, emissions and high fuel costs just don't justify it anymore. I had thought about the new 3.0 baby Duramax but honestly I don't care for some of the designs GM put into it. I just don't think that engine will age well and I tend to hold onto my trucks for quite some time.

I got to admit, it feels really good having my truck at 100% again. Thanks, Dean