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-   -   Lb7 going crazy electrical ecm? Bcm? (https://www.duramaxdiesels.com/forum/showthread.php?t=78476)

Dukchunter 01-12-2018 04:40 PM

Lb7 going crazy electrical ecm? Bcm?
Let me say that I have been using this forum for years and just now joined do to an issue that I have not been able to solve by searching the forums.
Here is what is going on.

Last week I started the dmax up it was a cold start( single digits) truck fired up, drove about 30 miles shut it off came back and fired it up 2 hours later drove 5 miles shut off fired up about hour later drove 35 miles. All with no issues as it always has. Came back to it 2 hrs later fired it up and it shut back off in about 2 secs, retry same thing, did this about 5 times, checked fuses and was blowing fuel heater fuse, replaced several times kept blowing. This went on for about 15 min until boom fired and stayed running.
Here is where the baffling part starts, after starting got the message un known driver, service 4x4, abs light on, battery light on, brake service light comes and goes, randomly chimes, power door locks do not work. Power windows work intermediately , key fob does not work.edge will not connect to truck. Powers on but can't connect. Scan tool will not connect either

Here is what I've done so far.
Cleaned ground on driver side frame, checked that grounds on engine block and rear frame were good and tight. Replaced ignition switch ( was going bad anyhow)
Pulled fuse box and made sure no critters were in there causing problems. Un hooked batteries for 1 hr, disconnected edge all to no avail. Some of the symptoms have come and gone some stay everytime the truck startes different symptoms happen. I listed above what is consistant. I did get the edge to con next one time and it said that my truck was running an OS That was not supported....

I'm baffled and don't want to throw money at it. Any ideas would be great.

P.s. I know I look like a noon but I have researched this for probly 10 hrs over the last week and have yet to solve this.

Dozerboy 01-12-2018 05:17 PM

After blowing and replacing fuses like that you might have got something hot enough to melt. I would get a wiring schematic and start checking and load testing circuits.

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DAVe3283 01-12-2018 05:37 PM


Originally Posted by Dozerboy (Post 1089800)
After blowing and replacing fuses like that you might have got something hot enough to melt. I would get a wiring schematic and start checking and load testing circuits.


Look for all the circuits physically near the wires to and from the fuel heater.

The other possibility is when the fuel heater (or wiring to it) was shorting, you were dumping all that power into whatever was touching. So something seemingly unrelated could be damaged at this point.

If you have a different body computer, you can try swapping that in and see if things change.

Dukchunter 01-12-2018 05:55 PM

Thanks for the replys. I will check that out tomorrow hopefully. Could be a possibility that I didn't think of. The fuse popped instantaneously when ignition was turned on so not sure how hot it could have gotten but will definately check it out

Awenta 01-12-2018 06:19 PM

aftermarket radio?

Also try disconnecting the lead for the gpcm and heaters.

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Dukchunter 01-12-2018 06:56 PM

Yes aftermarket radio pioneer 5600 7 in touch screen.
Gpcm? What is that sorry if that seems dumb.

Truck does not have on star

joshd472 01-12-2018 07:34 PM

Gpcm is the glow plug control module

Dukchunter 01-12-2018 09:38 PM

Awsome will try that... I did have that apart when I did headgaskets. It's randomly thrown glow plug code since

Awenta 01-12-2018 10:44 PM

Disconnect the batteries. Take out the radio fuse and hook the batteries up again. Then start it up.

They can get real funky when the voltage drops.

Letís start simple

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Dukchunter 01-13-2018 12:18 PM

Ok so this is what I did today,

Un hooked the batteries pulled the radio fuse then hooked the batteries back up. Fired her up. No change in symptoms still getting abs light brake service light it comes on then goes off every 15 secs or so sometimes it stayed lit. Service 4x4 still displays, unknown driver still flashed. Still no obd com, replacing fuse had no effect.

Unhooked gpcm lead and fuel heater lead. Fuse did not blow for fuel heater while unhooked looks like I need a new fuel heater. Truck fired and symptoms still exists although check engine light is on now. Still no obd com.

Finally I traced the fuel heater wires from the fuse box to the fuel heater looking for chaffed/melted wires. (What a pain) I found nothing visual in the harnesses nor anything with the other wires in the harness.

I did find something on the duramax forum late last night
Here is the link

It soesnt explain the door locks and key fob not working but explains the abs, brake service light and no obd com issue.

Thoughts? Thinking of removing mine to see any visual damage/ corrosion?

Firefightkev 01-13-2018 01:19 PM

My key fob quit working from a distance but if i would get next to the truck drives side door and it would work sometimes. I looked high and low for an answer couldn't find what the issue was. Heck I even bought a new key fob and programmed it with the same result. I had bought the truck and I never looked at the batteries age. One battery was 5 years old and another 2 years old. Ever since replacing them i have no had an issue with the key fob working correctly. I dont know if this could be related or not but low voltage with do some weird stuff.

Dukchunter 01-13-2018 02:11 PM

Replaced the battery in the key fob. Still doesn't work... the power door locks do not work... even pushin the buttons on the door does not work. I have a feeling that what ever is going or happened put the security system in a fail safe mode but the pass lock light does not stay lit.

Firefightkev 01-13-2018 02:22 PM

Check the trucks batteries not the key fob batteries.

Dukchunter 01-13-2018 03:00 PM

Truck batteries are brand new replaced in march. Checked voltage on both yesterday and where around 13 volts each

Burn Down 01-13-2018 03:55 PM

Need to fix the OBD plug first...

Do you have power at the cig lighter plug in? It's on the same fuse as the OBD plug.

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