I was in Northern Quebec James Bay region on a logging road driving between 70-80 KM. The Brake warring lights flashed and I had a tone (Not a lock on Jet) the Hybrid went completely dead I had steering it was hard and brakes had to push a little harder learned this from this group. The vehicle came to a rest on the shoulder, decleration was like taking your foot off the gas. I was out of On-Star range and cell phone. I removed the key several times and tried a restart, no joy. I then decided to diconnect the main 12 volt battery under the hood, I left it disconnected for a few mins and then tried a restart, it worked. I though this might be just one of those many little things gremlins and it might be. I contacted a friend at GM and he said i would be smart to take it in and have the dealer have a look in case I had a wire rubbed through on the GMLAN Bus we have two of them so i did. My dealership is in the town of Pembroke Ontario Bitler Chev. Here is the report:

Insp and installed TECH 2 checked for codes 21 codes set within modules need time to determine source of fault.
Performed SDGM cal update warr code 45B12 and also reflashed SEQ code SO742. Charged battery and road tested vehicle following day. No codes set drove into town thru heavy rough areas. No fault found. Would like to test agian later. service Manager road tested, again no fault found. Customer to Take Vehicle, if issue occurs again, have vehicle towed in.

Codes
EBCM
C0561
C0572
U0100
U0125
U0074

SDGM
U1818
U1817
U0074

HCP
U189A

ECM
POAC7

TTFP
B0081

HCP
U1818
U0074
P1815

ECM
U1842
U1820
U1817
U1815
U180F
U0074

TTF
B2555
SDGM45B12

SEQ50742

Nut sure why I have so many codes after the battery was disconnected. I have driven the vehicle 2,400KM since the issue with no problems. GM has been great doing everthing they can, however it is only one occurance and like finding a needle in the hay stack. Still Love the Hybrid

 

twice. both times just driving along (but slower) and the thing just shut down. After a wait (I didn't fool with anything) it restarted and worked fine. that is when I had the trans wiring harness replaced and it has been flawless since. there is was TSB out on this trans wiring harness but I think it was for 2008's and it had "disappeared" from the TSB list I have access to but according to TSB doc 2279993 it sounds like you did the correct thing (make a mental note "just disconnect the 12v for a minute..jet!)

 

Ken, removing the battery will not clear the codes. Whatever went wrong set all the codes, but it was probably a single failure that cascaded through the systems. When he read them out he cleared them to see what you would capture again.
Most of those codes are "Lost communication with xxxx" where "xxxx" is another module or system.
Others are high/low voltage indications (I can't be certain, as my 2008 manual does not have these exact codes).
My guess (and this is only a guess) would be that something went wrong in the 300V to 12V interface and brought the 12v system out of range (low or high) for a moment, thus shutting down all of the intermodule communications and the vehicle did a graceful shutdown. Finding this glitch will be a mother...

 

Thanks Jet and Fjungman for your comments, I am going to keep my eye on it. Unless it reoccurs it will be hard to find or figure out what happened. To date GM has been very supportive as well as concerned. Still I love this truck.

 

I had a very similar experience twice while driving my 2007 non-hybrid Yukon. I was driving down a semi-rough washboard dirt road and the vehicle just died, everything electrical worked, bright headlamps, proper voltage, etc. but the vehicle died and wouldn't start. I figured it was a relay or something i couldn't easily fix so I had it towed to the dealer. they found nothing wrong but when speaking to the mechanic who is an off road enthusiast, when he found I was driving on a rough road he said Delco batteries are susceptible to vibration and heat(I'm in Arizona), he did additional testing on the battery and it did have some sort of internal short circuit on just one of the plates, he said the vibration loosens particles from the internal battery plates and they accumulate at the bottom of the battery, when enough particles have accumulated, voila, shorted battery and vibration accelerates this process(like a washboard road). this happened twice when the vehicle was less than a year old, after that the dealer switched it to a "spiral wound dry battery?" never had a problem after that.