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Discussion Starter · #1 ·
My truck is a 2007.5 Silverado 2500HD.

I have been battling an ABS issue with the front right wheel.
Today I disconnected both batteries, unplugged the wiring harness from the ABS, did a continuity test thru wheel sensor circuit, test showed an open circuit. Disconnected the wheel sensor harness at the wheel and the test showed an open sensor.
I reinstalled everything in reverse order.

Attempted to start the truck, normal lights illuminated on the instrument panel, heard chimes, heard relay clicking in the engine compartment, one oddity was a message that said...service four wheel drive, have never seen that before. No codes.

Any help greatly appreciated.
 

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Discussion Starter · #2 ·
An update. I have checked all the fuses. Disconnected both batteries and let sit for an hour and reconnected. No change. There are no exterior or interior lights, the electric door locks do not work, the dash gauges do not work, the gear selector indicator does not work. Removed and inspected the wiring harness plug on the EBCM, all pins look good, could find no loose wires.
Seems like there is a communication fault between the modules.

Any thoughts?
 

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At a minimum, check power and grounds to the EBCM. If you have any kind of a scan tool, scan to see if any codes in any module are present. You may NOT have the necessary communications to allow your truck to start.
 

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An update. I have checked all the fuses. Disconnected both batteries and let sit for an hour and reconnected. No change. There are no exterior or interior lights, the electric door locks do not work, the dash gauges do not work, the gear selector indicator does not work. Removed and inspected the wiring harness plug on the EBCM, all pins look good, could find no loose wires.
Seems like there is a communication fault between the modules.

Any thoughts?
Most of what you describe is on the GMLAN low speed bus. There are two data busses on this truck. The GMLAN low speed (a single wire bus) and the GMLAN high speed buss which I believe is a two wire bus. The GMLAN low speed buss uses a 7 volt reference. Since everything was working before you disconnected the ABS I would remove the ABS harness and see if that makes any difference. Don't have a wiring print in front of me but the single wire to the GMLAN low speed bus might be shorted out to ground. An open would give you faults but the other stuff on the bus would still be operational. This will also take out the climate control, turn signals, and steering wheel control to the radio and since it is with the security module, no ability to start. Dean
 

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Discussion Starter · #5 ·
Ron and Dean thanks for your help. There are no codes shown on my reader. Tomorrow I will disconnect the harness from the EBCM and see if I can start it.
I have been trying to find wiring diagrams for my truck, any suggestions? Gmupfitters has been mentioned but I can’t find where on the site to access diagrams.
 

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Ron and Dean thanks for your help. There are no codes shown on my reader. Tomorrow I will disconnect the harness from the EBCM and see if I can start it.
I have been trying to find wiring diagrams for my truck, any suggestions? Gmupfitters has been mentioned but I can’t find where on the site to access diagrams.
Ron is the guru on that. I have been able to find prints but auto prints are hard to follow compared to aircraft stuff. Not sure disconnecting the BCM is going to help here. It is the heart of the GMLAN low speed system. Lose that and no communication to the security module which means no start. D
 

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Ron and Dean thanks for your help. There are no codes shown on my reader. Tomorrow I will disconnect the harness from the EBCM and see if I can start it.
I have been trying to find wiring diagrams for my truck, any suggestions? Gmupfitters has been mentioned but I can’t find where on the site to access diagrams.
Also no codes means one of two things. Either no communication on the buss or you have a reader that does not give the detailed specific codes for your issue. Not all readers are created equally. Dean
 

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Discussion Starter · #9 ·
Ron and Dean thanks for your help. There are no codes shown on my reader. Tomorrow I will disconnect the harness from the EBCM and see if I can start it.
I have been trying to find wiring diagrams for my truck, any suggestions? Gmupfitters has been mentioned but I can’t find where on the site to access diagrams.
Go here: https://www.gmupfitter.com/light-duty-vehicles/light-duty-prior-to-2013/

And find your year. then look for general instructions (pickups and chassis cabs), click on that, then electrical will show up as one option.
My reader is an older Acron unit.
Ron I have downloaded the electrical section. Wow great info. i Have needed this for a long time.
Not wanting to make matters worst and needing the truck this weekend I have carried the truck to the dealership. My local Duramax technician said this was the best thing to do and recommended one dealership with a good tech who has great electronic skills.

I will post what the outcome is so it may help someone in the future.
Thanks guys for your assistance.
 
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My reader is an older Acron unit.
Ron I have downloaded the electrical section. Wow great info. i Have needed this for a long time.
Not wanting to make matters worst and needing the truck this weekend I have carried the truck to the dealership. My local Duramax technician said this was the best thing to do and recommended one dealership with a good tech who has great electronic skills.

I will post what the outcome is so it may help someone in the future.
Thanks guys for your assistance.
Well at least yours is hard failed. Makes it much easier to find out what is the problem. Mine would intermittently drop the GMLAN low speed buss. Pulled my hair out for about 8 months before figuring out it was the aftermarket interface for the steering wheel control on my Pioneer stereo deck. Dean
 

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Discussion Starter · #11 ·
Well at least yours is hard failed. Makes it much easier to find out what is the problem. Mine would intermittently drop the GMLAN low speed buss. Pulled my hair out for about 8 months before figuring out it was the aftermarket interface for the steering wheel control on my Pioneer stereo deck. Dean
Still waiting to hear from the dealership. Last time, Friday, I heard from them they had it running but were trying to run down some other gremlins.
 

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Still waiting to hear from the dealership. Last time, Friday, I heard from them they had it running but were trying to run down some other gremlins.
With a hard fail normally you start unplugging modules till the buss comes back active (basically you can start the truck as long as it is not the BCU or the security module). One thing, one problem area on these trucks is the remote module on the crew cabs. This is located back in the aft pillar on the driver side. If you see issues usually related to rain this can be your problem. GM put a service letter out about it. What happens is water leaks thru the 3rd brake light above the cab and will follow a channel down that then drips in the aft corners of the cab. This is where that remote module is located. If it shorts out and brings down the GMLAN low speed buss you won't be able to start the truck. Curious on what they find. Dean
 

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Discussion Starter · #14 ·
A subscription to ALLDATADIY.com is very useful. You can also get information direct from GM for a short-term subscription of about $25 for 2 days last time I looked at it.

Also, bookmark this page to lookup GM bulletins about specific DTC. This list is not current as best as I can tell. But still very helpful.
Chevrolet Diagnostic Trouble Code (DTC) Definition, Causes and Diagnosis
Ron thank you for the links. I like to have technical info on hand, comes in handy when there’s problems.
Well the GrayGhost is back in her stall. The fix was a new BCM. Ouch!! I guess that’s better than spending hours searching for bad wiring inside a loom somewhere. I was hoping it might have corrected a couple of issues that were pre existing, tpms issue and a non functional windshield washer pump. But no luck there.
So do any of y’all have any idea what I may have done to cause this? I disconnected the wiring harness from the EBCM and the two wire connector leading to the right front wheel speed sensor, all done with both batteries disconnected. I think about some sort of weird voltage build up that spiked when I reinstalled the harness. I think about the ohm meter voltage but the only pins the leads were connected to was the two wires to the wheel speed sensor and that voltage should not be high enough to harm anything.
I just don’t know.



My mechanic friend thinks the truck would probably run even with the EBCM disconnected. The wiring info provided by Ron indicates that a portion of the abs signal does run thru the BCM. Sure would like to know so I don’t do it again.
 

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I have read that some BCM problems occur from disconnecting the BCM without disconnecting both batteries. Other than this thought, I don't remember the details of the post, sorry.
 

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Discussion Starter · #16 ·
With a hard fail normally you start unplugging modules till the buss comes back active (basically you can start the truck as long as it is not the BCU or the security module). One thing, one problem area on these trucks is the remote module on the crew cabs. This is located back in the aft pillar on the driver side. If you see issues usually related to rain this can be your problem. GM put a service letter out about it. What happens is water leaks thru the 3rd brake light above the cab and will follow a channel down that then drips in the aft corners of the cab. This is where that remote module is located. If it shorts out and brings down the GMLAN low speed buss you won't be able to start the truck. Curious on what they find. Dean
Thanks for the heads up Dean. When you say remote module is this in reference to the remote start feature?
 

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Thanks for the heads up Dean. When you say remote module is this in reference to the remote start feature?
Yes, everything that your remote fob does, lock, unlock, start etc.....This also is the module that receives your TPMS sensors inputs. Dean
 

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Discussion Starter · #18 ·
TPMS..... interesting.
 

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Here is a Youtube video that explains it. Dean

He is labeling it as a CAN bus which it is not. CAN busses came out later. The LMM series has two communication busses. The GMLAN low speed and the GMLAN high speed. The video is related to the low speed bus which is a single wire 7 volt reference bus. D
 
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