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I've done some searching through here and found a few different threads that are some what similar to my situation... but it's been inconclusive.

Recently the car, an 08 G8 GT, has been acting up with increasing frequency. The check engine light comes on during start up, car stuck in 2nd. If you clear the codes with the car running you can drive it normally, but upon restart -sometimes- it gets stuck in 2nd again. Sometimes a P0700 code populates with the U0073 code, along with a C0196-(xx) code that is a yaw rate sensor. The U0073 code is the only one that is consistent.

I've done the battery bolt fix that everyone likes to link to, sanded down/replaced the bolt on the chassis ground connection @ the battery-chassis, engine-chassis, and PCM/ABS-chassis. Issue persists.

Had the battery tested at AAP, came back as "better than spec" per the sticker.

Pulled major connections points apart and cleaned with electronics clear, let dry for a day then reconnected (PCM, ABS, Transmission 16pin, and the multipack connections near the fuse block and brake booster). Issue persists.

I've seen a few threads point to the valve body, or TCM being faulty but that doesn't seem to be consistent with 'clear codes, drives normally until restart' type condition.. anyone have experience with something like this before?
 

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Have you gone into Engineering mode and checked the voltage when its running?
 

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First find the sub codes after the U0073 either 00 for control module, or 71 for hi speed comm. or 72 for low speed communications, most likely the TCU, as P0700 always sets with trans issues as the trans always tells the ecm to set P0700 when it faults. Best bet is to remove trans connector and jam dielectric grease in that connector after inspecting it for obvious reasons. C0196 has always been erroneous among GM vehicles, A Tech 2 will show the module not communicating in the module communications data when issue happens
 

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Discussion Starter · #6 ·
First find the sub codes after the U0073 either 00 for control module, or 71 for hi speed comm. or 72 for low speed communications, most likely the TCU, as P0700 always sets with trans issues as the trans always tells the ecm to set P0700 when it faults. Best bet is to remove trans connector and jam dielectric grease in that connector after inspecting it for obvious reasons. C0196 has always been erroneous among GM vehicles, A Tech 2 will show the module not communicating in the module communications data when issue happens
I pulled and cleaned it with electronics cleaner, nothing stood out as noticably faulty, is there a telltale sign that I'm looking for here?
 

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As long as no pitted greenish whitish looking crust appears on terminals and terminal retention is tight you are good, but when it comes to data wires, they like a super tight sealed connection, Dielectric Grease packed connectors were GMs answer for many bulletins pertaining to data streams, and fixed most very well, you will prob be replacing the TCM if that fails, a tech 2 in its module data really eases the pain in finding the lone module when it drops out in real time
 

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Discussion Starter · #8 ·
As long as no pitted greenish whitish looking crust appears on terminals and terminal retention is tight you are good, but when it comes to data wires, they like a super tight sealed connection, Dielectric Grease packed connectors were GMs answer for many bulletins pertaining to data streams, and fixed most very well, you will prob be replacing the TCM if that fails, a tech 2 in its module data really eases the pain in finding the lone module when it drops out in real time
Wish I had the tools to reprogram those myself. Oh well I suppose.

I appreciate your help with all this!
 

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When mine did this, it was a short in the Onstar/Bluetooth box in the trunk. Threw the whole system into this error condition. I left it disconnected for a while and never came back. Once I reconnected it, the problem showed up again within a day. I ended up buying an exact replacement off eBay and it’s been fine. I didn’t bother programming my VIN as I don’t have Onstar anymore. I only use it for the phone.
 
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