What to do with extra High Speed GmLAN lines

[triggerdcrusader]

Yeah me again, with electrical. Again :|

So I'm almost done my LBZ to 2012 Avalanche transplant, but I've run into yet another problem. so the J1939 lines for LBZ are all self contained in the engine harness and only go between the ECM TCM and GCM. @kidturbo gave me some insight on how to use an LMM ECM to convert from 1939 to GMLAN which seems to work on paper, however the LMM is also self contained in the wiring harness, commands and information travel to the instrument panel and BCM via Class 2. The diagrams for the Avalanche are similar regarding the Class 2/LoGMLAN and high speed GMLAN, except EVERYTHING has both, so I've got 4 pairs of high speed coming out of the firewall coming from the Avalanche BCM that originally connected to the Avalanche ECM and TCM, with nothing to connect them to on the other side. what do I do with these? the wiring schematics show them simply spliced together all over the place so should I just connect them back on themselves? should I leave them cut?

on top of that I have a dark blue wire from the avalanche labeled "accessory wake up" going to Instruments, BCM, ECM, and TCM with nothing like it on the Duramax side. Any insight on to what these wires exactly do or even just a place to find the info myself would be greatly appreciated.


And one more thing; after reading the wiring diagrams until my eyes bled and trying to figure out how CP shutoff works I'm under the impression that as long as the engine is wired correctly, I can simply cut power to the run/crank relay to shut off the engine even if my Avalanche body I'snt 100% sorted out. I'm just afraid of testing it, and then having the engine run away because it doesn't have all of its inputs to the body set up. Am I stupid or letting paranoia get the better of me or both?

 

[kidturbo]

so I've got 4 pairs of high speed coming out of the firewall coming from the Avalanche BCM that originally connected to the Avalanche ECM and TCM, with nothing to connect them to on the other side. what do I do with these? the wiring schematics show them simply spliced together all over the place so should I just connect them back on themselves? should I leave them cut?

on top of that I have a dark blue wire from the avalanche labeled "accessory wake up" going to Instruments, BCM, ECM, and TCM with nothing like it on the Duramax side. Any insight on to what these wires exactly do or even just a place to find the info myself would be greatly appreciated.

The twisted canbus wires route a bit differently on the Duramax from a gasser.

First forget the J1939 points, LBZ didn't have it, unless you have an ECM from a 4500. So off the ECM you have a couple twisted tan wires, those are what ya want. Now in the Dmax, those ran straight to the GPCM on the engine, and the down to TCM. So if you remove the glow plug module, you cut the connection the TCM. Continuity tester is your friend here to trace everything out.

First check the wires coming from BCM, and you will find those 2 pairs are actually connected inside the BCM. If so, just pick a pair and tuck the others away. Same goes for the wires between ECM, TCM, and GPCM, shout all share continuity. The ECM has a 120ohm resistor built in, which you will see if check between CANhi and CANlo.

Once you have that sorted, in your chassis harness for the Dmax, you should find the two can wires that go to the ECM. Connect those to the ones from BCM and done deal.

The blue Wake Up wire from BCM goes to a matching Blue wire on the ECM, and also the TCM.. Exactly as is called, it Wakes Up the other modules by sending 12v when you turn on the key. In stand alone setups, we just tie that to the Key On wires power the ECM. But you want that going to BCM as GM designed it, then all the modules will work and speak as designed.

Hope that helps.

 

[triggerdcrusader]

The twisted canbus wires route a bit differently on the Duramax from a gasser.

First forget the J1939 points, LBZ didn't have it, unless you have an ECM from a 4500. So off the ECM you have a couple twisted tan wires, those are what ya want. Now in the Dmax, those ran straight to the GPCM on the engine, and the down to TCM. So if you remove the glow plug module, you cut the connection the TCM. Continuity tester is your friend here to trace everything out.

First check the wires coming from BCM, and you will find those 2 pairs are actually connected inside the BCM. If so, just pick a pair and tuck the others away. Same goes for the wires between ECM, TCM, and GPCM, shout all share continuity. The ECM has a 120ohm resistor built in, which you will see if check between CANhi and CANlo.

Once you have that sorted, in your chassis harness for the Dmax, you should find the two can wires that go to the ECM. Connect those to the ones from BCM and done deal.

The blue Wake Up wire from BCM goes to a matching Blue wire on the ECM, and also the TCM.. Exactly as is called, it Wakes Up the other modules by sending 12v when you turn on the key. In stand alone setups, we just tie that to the Key On wires power the ECM. But you want that going to BCM as GM designed it, then all the modules will work and speak as designed.

Hope that helps.

Okay, I'll look into that. The wiring diagrams I have must be from an lly or something. I have found that previously on Mitchel diy. Maybe that's why it's confusing. I did a keyword search for "wake" but nothing came up. The dmax wires might be labeled as something else, so I'll look again.

I'll see if I can get a diagram to help me out, but from what you said it seems pretty straightforward. I'll let you know how it works out. Thanks so much again man!

 

[triggerdcrusader]

The twisted canbus wires route a bit differently on the Duramax from a gasser.

First forget the J1939 points, LBZ didn't have it, unless you have an ECM from a 4500. So off the ECM you have a couple twisted tan wires, those are what ya want. Now in the Dmax, those ran straight to the GPCM on the engine, and the down to TCM. So if you remove the glow plug module, you cut the connection the TCM. Continuity tester is your friend here to trace everything out.

First check the wires coming from BCM, and you will find those 2 pairs are actually connected inside the BCM. If so, just pick a pair and tuck the others away. Same goes for the wires between ECM, TCM, and GPCM, shout all share continuity. The ECM has a 120ohm resistor built in, which you will see if check between CANhi and CANlo.

Once you have that sorted, in your chassis harness for the Dmax, you should find the two can wires that go to the ECM. Connect those to the ones from BCM and done deal.

The blue Wake Up wire from BCM goes to a matching Blue wire on the ECM, and also the TCM.. Exactly as is called, it Wakes Up the other modules by sending 12v when you turn on the key. In stand alone setups, we just tie that to the Key On wires power the ECM. But you want that going to BCM as GM designed it, then all the modules will work and speak as designed.

Hope that helps.

Okay, so I bought two other licenses on Mitchel diy and the good news is yes you're right, there is no j1939 running in the LBZ, but no, it does not have a wake-up voltage. The LMM harness however does. This doesn't post too much of an issue, except there's wake up voltage going to the lmm TCM and GPCM as well, and nothing on LBZ. There is however class 2 serial going from the ECM to all those other modules on the LBZ, as well as to all the LBZ body modules. So the LBZ has both going to pretty much everything except for smaller modules like door modules and stuff, but the lmm only has low speed, or high speed GMLAN going to everything except big things like the ECM, BCM, communications module, radio, etc.

So running the LBZ GPCM and TCM, that both have class 2 coming from the ECM up to a LMM ECM with no class 2/low speed GMLAN, will I have issues? As class 2 is just a collection of spliced data lines, can I just leave them disconnected?

And regarding to wake up signal, I can run an extra pin into my LBZ connector so that the pin on the LMM ECM can be connected to the rest of the Avalanche wake-up circuit, but that leaves wake up for the LBZ TCM and GPCM not covered. How are they powered on? Is that what the low speed class 2 is for on the LBZ? Is it manually by the pink ignition circuits? I've got like four different ignition 1 voltage wires going in but I have no way of telling what each of them do.

PS: thanks so much for all the help I get, it's really discouraging sometimes, and the more I try to figure it out, the more confused I get. It's really comforting knowing all you gents have more knowledge in this kind of thing.

 

[kidturbo]

The Class 2 data is where it gets tricky, cause GM ditched it in like 07, and everything after has only High Speed GMLAN there after. It was a single wire CANbus data line, that I never really took time to learn all it's functions. Main reason I suggested upgrading to the LMM version, everything else in your vehicle runs on the High Speed CANbus lines.

If your plan is to go with the LMM ECM and TCM combo, then you'll want to use that "Serial Data Wakeup" line as would be wired in LMM diagrams. And yes you can just add the pin to the harness if it is missing. The other pins to compare are MAP, and MAF I believe are slightly different. Been a while since I've done one.

Ultimately if you could find a LMM chassis harness, would make the job simple. If not, you will need to compare pin for pin between the two and adjust what's needed.

 

[triggerdcrusader]

The Class 2 data is where it gets tricky, cause GM ditched it in like 07, and everything after has only High Speed GMLAN there after. It was a single wire CANbus data line, that I never really took time to learn all it's functions. Main reason I suggested upgrading to the LMM version, everything else in your vehicle runs on the High Speed CANbus lines.

If your plan is to go with the LMM ECM and TCM combo, then you'll want to use that "Serial Data Wakeup" line as would be wired in LMM diagrams. And yes you can just add the pin to the harness if it is missing. The other pins to compare are MAP, and MAF I believe are slightly different. Been a while since I've done one.

Ultimately if you could find a LMM chassis harness, would make the job simple. If not, you will need to compare pin for pin between the two and adjust what's needed.

Yeah, with the new diagrams and your advice things are finally falling in place. Should have it turning over and this week.

I was actually talking to my boss about that one. He mentioned that now that we've done it once if we ever did it again it would be simpler, but I said to him just go with a full lmm chassis and swapping LBZ block into it, or get an LBZ roller, and get an lmm harness from some scrap yard. That one would have actually been mostly plug and play, even the inline harness and splice pack connectors are identical for the lmm, and the Avalanche. They just trade a few pins around for stuff like glow plug signal, wait to start, and that kind of thing.

Pay $2,500 for a race harness, maybe an extra couple hundred for the splice pack, and a fuse panel off of eBay, and your set. Much better than paying me hours and hours to disassemble and rewire the whole thing. Doesn't help that I don't really know what I'm doing either lol. I'm only 19 gimme a break.

But yeah, if I did it again, say for my dad who wants to duramax his H2, I would definitely set up the body and frame separate, maybe with those gauges you mentioned, save myself some headache. It would likely be simpler anyway because of the LBZ being the same generation as his gas truck, running on class 2 and all.

Thanks so much @kidturbo , I'll get you a video of it when I get her cranking. Least I can do for all your help.

 

[triggerdcrusader]

The Class 2 data is where it gets tricky, cause GM ditched it in like 07, and everything after has only High Speed GMLAN there after. It was a single wire CANbus data line, that I never really took time to learn all it's functions. Main reason I suggested upgrading to the LMM version, everything else in your vehicle runs on the High Speed CANbus lines.

If your plan is to go with the LMM ECM and TCM combo, then you'll want to use that "Serial Data Wakeup" line as would be wired in LMM diagrams. And yes you can just add the pin to the harness if it is missing. The other pins to compare are MAP, and MAF I believe are slightly different. Been a while since I've done one.

Ultimately if you could find a LMM chassis harness, would make the job simple. If not, you will need to compare pin for pin between the two and adjust what's needed.

Ok, so I have some good News and some weird news... Good news is she cranks, and runs, but only when the relay is fired manually, Its in the picture attached. So a few issues have arisen and I cannot figure out what is going on. I drew out how I rewired the circuits.

The only wire powered other than battery positive voltage that goes to the engine control module in accessory position, is the blue module wake up wire. So I have a feeling either that, or some GMLAN signal is being misinterpreted, but correct me if I'm wrong.

Have you ever run into anything like this, and is there anyone you can point me to who could help me solve this problem?



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[kidturbo]

Are you getting any gauge data to the dash?

Do you have access to a good scan tool like SnapOn or Tech2? Need to verify the BCM and ECM are speaking.

 

[triggerdcrusader]

Sorry for the late reply had some trouble with my account signing out.

No, we have a budget tool don't even remember the brand, it's worked every time before, but When plugged into obdii, it just reads error1 which means it can't communicate with the modules. Dunno if that also means modules aren't communicating with eachother, because BCM is sending some kind of message to the ECM in accessory position that causes the engine to crank for a few seconds.

Dash does read some things like it says check coolant level (it's only half full) and the like, but it doesn't read any guages, no fuel level, no tach, and I have no way of testing speed yet.

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