LMM: Electrical issues again

Dstaub22

Dstaub22

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Jan 29, 2020
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Today while driving, my radio and gauges fluttered for a second and then Would turn off and stay off, but the truck would run. I just recently did an egr delete and had an airbag replaced if that helps any. The batteries are maybe 1.5 years old and I had them, and the charging system tested recently. I attached a photo to show what my gauges look like
ee1a86a8e68d9ac56791346e6af36543.jpg



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K

KyleC4

Tech
Dec 30, 2016
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Can you get codes? For gauges to drop and all telltales to turn on while still being powered up lead me towards a possible communication issue but I would like to have some codes to be a better help. Radio and IPC are both on low speed comm. line as well. That’s why I’m guessing that if you were wondering
 
ikeG

ikeG

Oughta Know Better
Apr 19, 2011
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Check the mega fuse connections on the passenger firewall, by the battery. They are known to come loose or corrode.

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Dstaub22

Dstaub22

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Jan 29, 2020
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KyleC4 said:
Can you get codes? For gauges to drop and all telltales to turn on while still being powered up lead me towards a possible communication issue but I would like to have some codes to be a better help. Radio and IPC are both on low speed comm. line as well. That’s why I’m guessing that if you were wondering
Click to expand...

I haven’t gotten codes pulled yet. My CEL light is on but the only reason I know is because of the #3 glow plug and I wasn’t having these issues when the light first came on
 
Dstaub22

Dstaub22

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Jan 29, 2020
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Also, the truck will start up and run even if none of the gauges are communicating
 
Dstaub22

Dstaub22

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Jan 29, 2020
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ikeG said:
Check the mega fuse connections on the passenger firewall, by the battery. They are known to come loose or corrode.

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Click to expand...

Just checked them. They’re tight and clean. I just tried to crank it, and I turn the key to accessory and all lights come on, regular sounds and everything. But the engine won’t even turn over.
I’m at a loss
 
ikeG

ikeG

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Communication codes will probably be what you have. Will narrow it down to certain module(s) hopefully. Then you might need schematics to see power sources or whatever it points you towards

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Dstaub22

Dstaub22

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Jan 29, 2020
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ikeG said:
Communication codes will probably be what you have. Will narrow it down to certain module(s) hopefully. Then you might need schematics to see power sources or whatever it points you towards

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Click to expand...

So this has the possibility of being more than just a simple loose ground or faulty relay/connector?
 
DAVe3283

DAVe3283

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Sep 3, 2009
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It could well be a broken wire or a bad ground on a module causing the bus to not work right. But it could be a failed module crashing the bus. A good code reader will helpfully at least let you see what is and is not communicating, and start narrowing it down.
 
ikeG

ikeG

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Apr 19, 2011
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Well there's always the possibility but I doubt it. If you cant find a problem by just checking 'everything ' the DTCs can be next thing to direct you.

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J

JimmyMac

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Sep 1, 2015
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Different problem - Simmar issues

For some time I have been receiving strange status displays. Started with “Range Shift Inhibit” and resulted in complete losses of movement. Let it cool off for 12 hrs and took it if orvservice. Worked ok for about a year, happened again in St Louis (raining like a monsoon). Took it to an Allison service shop. After $600 service (deeper pan, change of fluid, and weatherproofing connector) worked fine for another year. Next few occurrences found if I turned it off, restarted it worked for a while. Then I got a number of strange issues that would not go away “Service Brake System, and others) and they would not clear even after service. Decided to take it to local Chevy Dealer. After $1200 (and a lot of excuses), they stated it was a wiring problem. Worked for about 2000 mil, then returned. Took it to Wills Cadillac GMC in Iowa, after $800 they said it was an improper splice and a bad connector. So far it has been fault free for the last 5000 miles. Suggestion - wish I had one. If you have a dealer you trust, suggest a complete diagnostics. Makes you want to move back to the simpler days
 
Dstaub22

Dstaub22

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Jan 29, 2020
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I read the codes I’ve got with just a basic scanner, and I got p0673, p154b and p154d. Nothing too serious but I recently deleted my EGR so 154(b,d) are related to that delete. I haven’t been able to run a deeper diagnostic but as far as looking around, I’m not good with the electric standpoint of wires and grounds so I have no idea where to start


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Dstaub22

Dstaub22

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Jan 29, 2020
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Also it’s running fine now. It’s actually acting as if nothing was ever wrong. No low voltage, no “no crank no start” everything is working as it should. I’m guessing it could be one of the modules because it’s done this before and I’ve left the batteries disconnected for a few hours the other day and it was back to normal. Unless that’s just me jumping to conclusions thinking that resetting the ECM/TCM is fixing the electrical issues via bad communication


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