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Discussion Starter #1
223000 miles without electrical problems, but halfway out the driveway today it shut off and refused to start. I have a code u1800 for no communication between ecm and ficm. Preliminary check on the wiring and fuses revealed nothing, but I don't have power on pin 118 Injector supply voltage at the FICM. Is this my problem? Any idea where I need to go to fix it? I don't have identifix anymore and have been all over google, but can't seem to find anything. Going to attack it in the morning, just thought I'd give yall a chance to help with it!
 

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So the wiring all seems fine, so I ordered another FICM. I'll have that and install it tomorrow and update this then. Let me know if you have any ideas between now and then!
 

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Moved to LB7, you will get more response there.

Have you checked the fuses- with a test light?? there are two different one to power the electronics- Check the ECM harness for wear and shorts. Some have had a short at the connector to the FICM, Do you have anything connectewd to the truck, like a old Edge- if so, try it with those disconnected-
 

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Thanks, I wasn't sure where to put it. I checked all of the fuses under the hood with a multimeter. I can check the inside ones as well if they are involved at all. I looked over the harness and didn't see anything. I will check the plug a little closer. I have an insight cts2 on that has been there for a while now. Ill try it with that unplugged.
 

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I've had fuses that tested good with a multi meter that were in fact bad.
 

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Thanks for the info. I rechecked the wiring and fuses and installed the new FICM. The truck fired right up on the fist try and then did the same thing just a little later. I opened the old one and found a burnt terminal inside. It looks like pin 114 which is ground. Any idea why that would have happened?
 

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I went back out and rigged a ground to the case of the one that is currently in and the truck started. Now I am wondering how I managed to overload that circuit. Is there a loose ground? Where is the FICM grounded? Does it usually ground through the case? Seems unlikely, but maybe it lost ground that way. Just chasing my options, Thanks for the help!
 

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I opened the case up and found that one of the ground terminals had burned off internally. I ran it for a little bit with that ground on the outside and then it burned that off also! I am really confused as to where all this power came from, that was a 14 ga wire! Any ideas are appreciated, I am kinda scared to try anything else after that!
 

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Thanks for the info. I rechecked the wiring and fuses and installed the new FICM. The truck fired right up on the fist try and then did the same thing just a little later. I opened the old one and found a burnt terminal inside. It looks like pin 114 which is ground. Any idea why that would have happened?
Possible the body grounds are not making good connection, and trying to ground through the ECM/FICM. Check the one under the cab on the driver's side, and the one back of the engine head. Do to our have any other crazy electrical showing- headlights-etc

Sent from my Moto G (5) Plus using Tapatalk
 

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Thanks for the input. I wiggled them and checked them visually. The only thing that I could find was that the one on the firewall was corroded. I will work them over a little more and replace the corroded one.
 

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Possible the body grounds are not making good connection, and trying to ground through the ECM/FICM. Check the one under the cab on the driver's side, and the one back of the engine head. Do to our have any other crazy electrical showing- headlights-etc

Sent from my Moto G (5) Plus using Tapatalk


^^^ this is good advice, You may even want to take it a step further and do "the big 3" (which is more like a big 6 on our trucks) and upgrade the frame to - ground, engine to - ground and alternator to + lug on both batteries with 0 gauge wire. That is the tried and true solution to MANY chevy problems. The factory grounds are just way too small and over time, corrosion, rust ect cause those grounds to become even worse which allows current to find its own path to ground which unfortunately some times means flowing through other components. The firewall ground strap is also VERY important and should not be overlooked, however failure of that ground usually toasts modules inside the dash.
 
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