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Discussion Starter #1
i have a 05 gmc lly and this is the second time the engine has shut down while driving do the road. The first time it happened i did some research and said to check the wiring harness to the FICM. So i did check it and did not see a problem still no start checked for codes and none there, it sat for a few days till the weekend so i could work on it. I went out and tried to start that weekend and it fired right up. I have no idea what changed so i started driving it again about 3 months later it did it again driving down the shut off like someone turned the key off. i had it towed to my job rechecked the wires still did not see a problem and it did not start. it sat for a week and now it starts again. i am at a loss and beginning to wonder if the FICM could be the problem! i spoke with my Buddy that works at Chevy and he say he keeps these in stock and sells them often. Any help with this would be greatly appreciated because i am afraid to drive it again and it leave me stranded. I don't want to buy a 1100.00 part and it not fix it.
Thank you for you help
John
 

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Codes?
 

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The worst thing that can happen is to have your truck "heal" itself. It's pretty hard to fix something that isn't broken.

Try heating the FICM with a blow drier and see if it shuts off again. From what you have said, all it takes is a cool down cycle and it runs again.

You have two choices at this point. Drive it until it fails again or take a guess at what is wrong and throw a part at it. $1100 is a lot to throw though. Maybe a know good used part would be cheaper and more sure.
 

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Are there any particular conditions that will make this happen or is it just random?
 

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Discussion Starter #5
it does have a code u0105 which loss communication with Ficm. i have checked all the wires for any bare spots. i also took it to a gm tech and he also checked the wire and pin connectors at the Ficm and didn't see anything wrong.
 

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Discussion Starter #6
that is a good idea i will try to heat it up and see if it causes it to happen. I hate having a problem i cant find and something that doesn't stay broke so you can find it.
Thank you
 

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Discussion Starter #7
Just random, it has happened twice now and i haven't driven it since for any length of time because of not knowing when it will shut down.
 

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I assume you did check the FICM harness where it is secured with a tie at the FICM bracket- common place where the sharp corner of the bracket cuts into the harness and wires.

The FICM has a vent hole and some spray the engine with water to clean it - water then gets inside the module and causes problems.

Do you have an old model Edge connected--?? Many have had problems with that part where iot is connected to the main harness. The Edge unit itself was the problem with killing the engine.
 

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Discussion Starter #9
Yes i have checked everything that i know to check. I have seen comments about an EDU fuse which i cant find all i have is and Edu relay in my fuse box. My harness before was not even strapped to the bracket like it describes, it has had some TSB's performed at the dealer years ago so i don't know if they already took care of that problem while they were doing the injector harness. i have never washed the engine with water and i don't have an Edge system i have Efi live with the switch.
 

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Discussion Starter #10
I worked on the truck this weekend, took all of the wire loom and tape off and did not see any bare spots in the wires. I started the truck and shook and moved all of the wires and harness around to see if there was a shorted wire that would cause it to shut off and nothing happened. I then took a hair dryer to heat up the FICM to see if it got hot and shut down and that did nothing so i am still at square one and don't know what else to do. is it possible for the FICM to have an intermittent problem? Any help would be greatly appreciated would like to feel confidant in driving my truck again.
 

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Define "won't start"

Motor turns over, but doesn't fire off and run?
Or
Turn the key and nothing?
 

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Discussion Starter #12
After it happens the engine turns over just fine but does not run it can sit for a few days and then it will start. Crazy
 

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Anything displayed in relation to the theft deterrent?
Any loss of prime at the filter head?

Ruling out all the other fuel related and no codes, all I see left in historical ('bout 100 related threads-with all different shut down causes), are different triggers for BCM related shut downs. Security or a random wire short/arc.
 

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Discussion Starter #14
no theft and plenty of fuel does have the code u0105
 

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U0105 indicates loss of communication between the ECM and FICM over the GMCAN bus. The GMCAN bus is used by many modules on the truck. Each module has its own code so the other modules are communicating just fine. Only the FICM has problems. No FICM = no start. The computer has told you what the problem is.

I would begin by clearing the code and see if it comes back. You can't really diagnose much until it loses contact and sets the code again. If the code doesn't come back quickly then I would drive it with a scanner and some testing equipment aboard until it has the problem. Then I would scan it for a current code. If the code is current then I would do the testing, even if it is at the side of the road. It is MUCH easier to fix a problem when it is current.

You are going to need a wiring diagram and connector views with pin-outs.

The diagnosis for this code starts with testing all of the FICM power supply lines, both battery and ignition.

Step two is to check all of the grounds.

Step 3 is to check the GMCAN lines for shorts to ground or power or for opens.

Step D is to replace the FICM.
 

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Discussion Starter #16
Yes everything else is working fine when this happens. it has happened twice being months apart and has come up with the same code U0105.
 

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Discussion Starter #18
Thank you i will take that area apart and look at that side of the harness. i would defiantly like to find a problem so i am not chasing a ghost and spending a ton of money on a FICM. i will let you know what i find.
Thank you
John
 

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Discussion Starter #19
I rechecked the harness again along with taking apart the two big plugs on the driver side of the engine and checked for any bare spots on the wires coming out of it and nothing found bad. It has been running fine, but i have not been driving it around because i don't want it to leave me stranded at the wrong time. I am still at a loss and might look into purchasing a remand FICM to see if that changes anything.
 

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Discussion Starter #20
I am still having some problems with my truck. I recently had it running and driving and everything was fine, parked it for a few weeks and went to start it and it spins over no start. i found a leak at the fuel filter head i replaced the seals and still leaked so i put a new one on it. it tried to start ran for about 3 seconds and shuts down i am thinking it was air bound. I planned on putting a lift pump on anyway so i did and it started and ran. But now i have a code p0611 could my Ficm finally be going considering the other problems i have been having with the U0105 code i have had in the past?
 
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