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Discussion Starter · #1 ·
So I have a transmission communication issue that has been twice declared to be a wiring issue. I figure instead of pulling my hair out searching for it, I would simply get another harness altogether. I found a couple donors that will fit, but the yard is very far away. I'd like to avoid that distance if I can. The yard I usually go to has a few of the same engines, but cross referencing on a GM parts site says it won't fit, which is just strange to me.

My car: 2006 Buick Lucerne CXL 3.8L V6 (Harness Part# 15908453)
Possible(?) donor: 2007 Buick Lucerne CXL 3.8L V6 (Harness Part# 25813747)

I should also note they use the same computer as well.

What is so different about this harness? Could I get away with using it? Perhaps it's just an improved part. What about this won't work?
 

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Clean your grounds (under coil packs and near starter), add some improved power/ground cables for ~$20 (alternator to accessory terminal, chassis/strut to engine block, etc.).

The TCM is more likely at fault than an undisturbed OEM harness, which you are about to climb all over the engine and disconnect/unclip to replace. More clarification on the actual issue is going to inform your actual need before you spend 2 days cutting your hands and inventing new profanities while trying to get at the entire harness in one piece (I do it on my modified car/harness, and it's still not fun).
 

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Discussion Starter · #3 ·
Clean your grounds (under coil packs and near starter), add some improved power/ground cables for ~$20 (alternator to accessory terminal, chassis/strut to engine block, etc.).

The TCM is more likely at fault than an undisturbed OEM harness, which you are about to climb all over the engine and disconnect/unclip to replace. More clarification on the actual issue is going to inform your actual need before you spend 2 days cutting your hands and inventing new profanities while trying to get at the entire harness in one piece (I do it on my modified car/harness, and it's still not fun).
This is fair, though I have no way of finding out if the computer is at fault. Three mechanics couldn't tell me. Also, it does not appear to use a TCM? This was confusing to me. I think it's all one computer? The ECM is located in the airbox and it's completely alone. Internet part searches tell me there is no TCM.

The reason I'm doing all this is because it's in limp mode. First gear is inoperable, second gear only works in the manual settings, and third gear also works, but is the only gear operating in automatic settings. It's not really drivable but it moves.
 

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Gotcha. I didn't look to see if it had switched to the newer 2 boxes or not. Sounds like a limp* mode or similar. Sadly, a dealer tech with a Tech2 scanner might be the best diagnostic bullet to bite.

My family/friends included, 95% of shop mechanics don't have the equipment or familiarity with the system details across all different models coming to them now. This is only going to be more common as OBD2 era cars, especially CANBUS era starting in ~04-05, get older and fail in more and more ways that have limited access to parts and information. This is why people have rallied around certain engine platforms for modding that aren't necessarily the latest and greatest (LS, SBC/SBF, B/D/K Honda, 5.0, 2JZ, 3800, etc.), since they're not as locked to OEM computers/sensors/parts for all but core items that are universal.
 

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Discussion Starter · #5 ·
That's where it gets worse, I DID take it to a dealer. They didn't bother the computer at all. Instead they're like "yeah we want to inspect the wires you repaired, and look deeper. Instead of the standard inspection charge, we want to charge you for an additional five hours of labor." That's right, they wanted $900 just to diagnose it! That's why I'm thinking it might be worth my time to swap the harness and the computer together, since they're so cheap at the junkyard. Now that you mention the grounds, I could try that first, though I know nothing about what makes the grounds go bad on these things. Could be the fact that I lost the splash shield some time ago. Incident with a deer, only lost the splash shield and a wheel well.
 

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Gotcha. Well, the grounds may just get corroded or loose or broken near the eyelet overtime. The splash Shields are mostly to protect things from corrosion, like the starter underneath or wiring and components near the wheel. Hopefully, you come across some things that need minor fixes to get you rolling again. Let us know.
 

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Discussion Starter · #8 ·
So I decided to just give it to one more mechanic. This guy found the issue. Apparently when I replaced the water pump in an effort to fix a leak, I bumped into a wire that was corroded, and it broke. He found it very quickly and had the car ready for me right away. Drives great now, but this could have been prevented. The main harness loom is crispy and peeling. It's mostly gone now, leaving wires vulnerable in many places. I'd like to re-loom the harness where needed and tape it up of course. I cannot find loom big enough at a parts store. They have 3/4" I need more like an inch or 1 1/4". Where can I find such loom??
 

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You'll have to look online (eBay and Amzn should have kits you can pick thru). Loom isn't a fan of long-term use like the 15-25yrs old these car are now, and tends to get brittle with time and exposure.
 
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