Possibly a Bad ECM?

Daryl LBZ

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I would load test them. The digital battery testers are not always accurate. I have both and got different results. A load test will tell you if the batteries are good under a load.


Ok. Is this where I would take the batteries to say Autozone and they put them on their machine?
 

Cougar281

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Sep 11, 2006
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I had SP205 out and checked it whenever the truck wouldn't stay running after I installed the tow mirrors. I found and still have a lot of information on this from last time. Last time I was getting the trouble code for Data Link Low which "usually" means a grounding issue which is exactly what it was because I had accidently grounded the purple wire coming out of the OBD2 port. Data Link High "usually" indicates an open circuit which could be a wiring problem, or one of the modules is bad and it will not stop constantly trying to communicate on the serial bus which in turn block communications with everything else. That's the way I understood it anyway, but from what you posted above is that not the case?
I'll have to look and see what SP205 is for on the 06 LBZ .. if it's a class 2 splicepack, then it should not have an impact on the engine running, other than possibly theft deterrent type comms with the BCM. A problem on the class 2 bus shouldn't take down the CAN/GMLAN bus.

I didn't note if you have efilive, but if you do, you could flash a VATS disabled tune in and see if it starts then... If it does start and run, then it could be a class 2 issue preventing theft deterrent comms... I can't see rooting around in the doors changing mirrors affecting much else beyond the class 2 bus...
 

Bdsankey

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This is from Bench Force. Does this seem to be the correct one for my truck?


View attachment 129871

I guess I would need this too for power.
You would need them both. That will set you back ~$600 or so with shipping. You have the LLY harness shown but the post is for an LBZ, I linked the proper LBZ harness below instead.

 

Daryl LBZ

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Jul 18, 2024
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You would need them both. That will set you back ~$600 or so with shipping. You have the LLY harness shown but the post is for an LBZ, I linked the proper LBZ harness below instead.



Thank you! I contacted the seller on eBay that was mentioned in a previous post and he does not have anything that will work for an LBZ ECM. I'm going to trouble shoot some more this weekend, and I will probably end up taking you up on your offer if your don't mind.
 

Bdsankey

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Thank you! I contacted the seller on eBay that was mentioned in a previous post and he does not have anything that will work for an LBZ ECM. I'm going to trouble shoot some more this weekend, and I will probably end up taking you up on your offer if your don't mind.
Just shoot me a PM and I will get you my address, no worries at all. I can help source a replacement if the time comes and update/program to your VIN.
 

Daryl LBZ

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Jul 18, 2024
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Just shoot me a PM and I will get you my address, no worries at all. I can help source a replacement if the time comes and update/program to your VIN.


I haven't gotten anywhere further yet. I had to do some regular maintenance to two of my other vehicles over the weekend first. I went out yesterday to load test my batteries and the one was about dead, and the other was at about 50%. So, I didn't even bother troubleshooting yet until the batteries are charged up. I plan on load testing the batteries and doing more troubleshooting after work on probably Wednesday night.
 

Daryl LBZ

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Jul 18, 2024
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UPDATE:

I decided to get my multimeter out and check all the pins in Splice Pack 205 (SP205). So with the comb pulled out of SP205 I'm getting 7.53v on pin B (ECM) and 5.95v on pin K (Generator Battery Control Module Class 2 Serial Data) which indicates a data link high condition from what I remember. If I remember correctly that indicates that either a module is bad and is constantly sending a signal, or a wire is messed up. Now when I unplug the ECM I obviously get no volt reading on pin B, but I still get the same 5.95v reading for pin K. Any idea what exactly pin K is for or what it does? Any idea if this is related to the ECM issues as well?
 

2004LB7

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How about pulling fuses for the different modules until the voltage goes away
 

Daryl LBZ

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I will try that tomorrow. The Generator Battery Control Module is throwing me off though. I would like to know why it has a high voltage signal as well.
 

2004LB7

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I will try that tomorrow. The Generator Battery Control Module is throwing me off though. I would like to know why it has a high voltage signal as well.
I'm not familiar with this generator battery control module. As far as I know, the ECM controls the alternator directly. It sends the signal to the regulator on the alternator to turn it on and off
 

Daryl LBZ

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Jul 18, 2024
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I'm not familiar with this generator battery control module. As far as I know, the ECM controls the alternator directly. It sends the signal to the regulator on the alternator to turn it on and off

That is what I'm reading as well. It just doesn't sit well with me ruling the issue to be with my ECM only whenever I'm getting a high voltage reading for generator control module as well. Unless this is normal then that would explain it obviously.
 

Daryl LBZ

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Jul 18, 2024
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I'm not familiar with this generator battery control module. As far as I know, the ECM controls the alternator directly. It sends the signal to the regulator on the alternator to turn it on and off


Ok so I did some more digging tonight and I found that I was looking at this wrong when it comes to pin K. So pin K can be three different things depending on the truck you have according to the wiring diagrams I have. Three different things also means three different wire colors. So for the Generator Battery Control Module the wire color at pin K would be Orange & Black. My truck doesn't have that obviously so it's not that option. I have a YELLOW wire which is for Allison Class 2 Serial Data.

So after finding this out I decided to unplug the TCM and recheck the voltage on pin K with my multimeter, and as I suspected I now have no voltage at the pin any longer. I then decide to plug my ECM back in and check the voltage for it at pin B. After rechecking I found that it is still putting out 7.53v which is WAY over what it should be.

So it appears that there is a problem with BOTH the ECM & TCM which seems very odd to me. They are both putting out high voltage at their respective pins in Splice Pack 205 which indicates a short to power. So that supposedly means that either the modules are bad, or a wire is rubbed through somewhere. Where that would be I have no idea, but it seems like I'm going to have to dig deeper into the wiring harness, pins, etc to make sure the wiring is ok. What a mess!
 

Daryl LBZ

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Jul 18, 2024
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Ok so I wanted to post an update in case someone else out there has a similar problem some day. So long story short, after being too busy to really dig into this thing really deep for a few months I've finally found the answer. Turns out it was just a loose ground wire bolt on the passenger side of the engine block. I had been over all of the grounds when I put this truck back together, so I sort of pushed that to the back burner as a possible issue. What threw me off was that the truck had ran and drove fine until the day it just decided to stop running. So obviously at some point the bolt backed out causing the ground to become loose. Thankfully I didn't spend any money to figure this out and I'm just happy that the truck is running again!