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08 CTS DI
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Discussion Starter #1 (Edited)
B3794 BCM- Cruise control function request circuit signal invalid.
U1826 EBCM- Lost communication with multi-axis acceleration sensor module .
U0101 EBCM-Lost communication with TCM.
U0140 EBCM- Lost communication with body control module.
C0899 EBCM- voltage low.

I guess it's my turn to toil. I had a terrible incident today. I had to baby sit the accelerator pedal for a 20 min hwy drive, because cruise did not respond on command.Control button light was illuminated, but no green light on instrument panel.

Research has revealed that usually the engine light along with several other bells and whistles pop up with any one, or more of those codes. I had none of that and investigating with the Technoid 2 revealed the above codes. They also appeared as "Passed" for "Last test" and "This ignition". This is the stopping point for now.

Relevant history; A few days ago I replaced the battery. During the process, I connected a small 6 Ah battery to the cable ends to maintain my preset radio stations. My suspicion is that this good will gesture may have lead to the problem, from the voltage drop, as opposed to complete loss of power, not unlike the kind of troubles that can result with a start attempt on a low battery, or driving with a bad alternator.

Other possibilities are:
Brake light sensor.

Stuck cruise button.

OBD II diagnostic port monitoring device (code reader, insurance co monitor, etc).

Bad BCM, resulting from the voltage irregularity. It seems far fetched, but I've read some threads that resulted in spontaneous BCM failure in and around alternator problems. I hope this is not the case with the passed test status.

Under hood fuse box problems, as they have been known to trigger some of those codes, as well as some other severe, intermittent problems from voltage swings.

Since there are no other indicators on the dash, aside from the TPMS light, and the car runs fine, I am hoping the problem will have resolved by next drive, having cleared the codes and pulled the BCM and ECM fuses, and if not, I may consider pulling the negative cable for a while before digging deeper..
 

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Discussion Starter #2
Test drove the car this morning and so far cruise is back to normal. So it appears the transient power support attempt is the likely cause at this point, since the communication BUS was still active during the battery change, as the trunk courtesy light was still on and went out when the cables were disconnected, shifting power support to the small battery.

I added two more possible causes to the list above, but from searches on the codes, B3794 is a good code to have in the presence of the others, because it tends to suggest a less in depth problem and usually when the other codes are present, you also get extra warnings on the console; stability, eng light, and ABS warnings. Since those warnings were absent, I leaned more toward the battery replacement as being the trigger point.
 

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Discussion Starter #4
sounds like now you have it sorted...good luck

Bill
Time will tell. I need to add that a scan tool capable of reading BCM codes was necessary for me to access the codes listed above. It is crucial in gaining some idea of what's going on, otherwise you can speculate out to "sea" relative to where the real problem is near by.
 

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FWIW, when I replaced my battery I had everything staged and ready for the actual swap. The total time the vehicle had without a connected battery was less than two minutes. No radio presets or DIC information was lost, but I did have to re-index the glass and performed the throttle relearn procedure.

I would surmise your codes were relevant to the battery swap or the interim power source, but I know you do not like to speculate.
 

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Discussion Starter #6
FWIW, when I replaced my battery I had everything staged and ready for the actual swap. The total time the vehicle had without a connected battery was less than two minutes. No radio presets or DIC information was lost, but I did have to re-index the glass and performed the throttle relearn procedure.

I would surmise your codes were relevant to the battery swap or the interim power source, but I know you do not like to speculate.
No problem with speculating, I'm just fearful of it, because if I'm wrong, that means a lot more digging that I'm in no mood to do. Now that you mention it, codes for re-indexing the windows were also present which was comforting and further pointed at the battery swap. The terminals were off for less than 2 min as I did so much staging it was changed before I left the store parking lot. I kept my old battery for projects and gave them an old dead Walmart special I had.

Although my car performs the throttle learn at every shut down, I performed that as well before the drive this morning and it became evident when the radio started up on AM, with my presets visible for FM, that they probably would not have been lost if all power had been cut, similar to what I did when I pulled both the PCM and BCM fuse after shut down yesterday.
 
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