Brian,
Is this a great forum or what LOL.
It will be interesting to see if a "NEW" module needs to be dealer programmed to match your vehicle (pretty sure it will?). Please update the forum (aka: the world) on that.
My area has a glutton of Two mode Hybrid units.I think they are starting to age out of value where the insurance companies will repair them and are simply getting junked out a lot more now.
Good news is parts are more available Bad news is they are now considered Junk LOL

 

Well I wasnt as lucky.... bought the gmoe part off Amazon for 150ish... had it put on, then took to dealer to flash.... and it's still at dealer so they can figure it out.. pray for me and I'll keep you guys posted.... I just knew after seeing your post this would fix mine. Exact same symptoms. Oh well.. we shall see.

 

Brian did you have the DTC Code C12D8?

 

Brian any updates on the repair? I am now at 227k I had a few trouble free miles but the ole taHOe just seems to want to continue to act out.
I recently had another code pop up, it is C129F and I only have the service brakes soon message not the ABS/Stabiltrac lights and the biggest thing is the brake boost has not stopped working with this code which makes it much less of a "panic" situation.
C129F seems to refer to a brake pedal position sensor (ACDelco Brake Pedal Position Sensor 25799118)
From what I am seeing my 2009 Tahoe Hybrid does NOT utilize that position sensor on the side of the power adjustable brake pedal assembly.
I see the spot for it to mount and it appears to never have been there from the factory? Figured it was something that some other GM models that have the power adjustable pedals used just not the Tahoe? I will post a pic of the actual mounting area on mine when I get a chance but it is on the lower left side of the power adjustable pedal brake assembly.
I cleared the code and it has not come back for a few days now. Anyone else ever seen this code???

 

So update here brakes out again this time I received many codes and lost brake boost again the codes indicated bad ABS assembly. I guess the previous ncode was a forewarning of trouble! Took it in to my local dealership service for diagnosis they said the ABS pump had died and module was bad. Parts are not available from GM Obsolete so they say. Ordered a replacement entire ABS assembly from a online used parts supplier in houston used unit with 134k miles. I had a local garage to swap it in and do the reprogramming. Now back in business at around $700.00 out of pocket later. Old high Mileage vehicles are troublesome and can be expensive..... now my drivers side power fold mirror has stopped working (infamous plastic gear issue) so next project is already lined up. Thinking about Gruven replacement gear and motor for the mirror but it looks like it might be a big hassle to install and is over 50 bucks for the parts. Sigh just never ends.

 

I am having this same problem with my 2009 Chevy Silverado, and despite reading every thread I could find on the subject, I never found a definitive cause. Is there one? For context, we live in a very small town on an island. Max speed limit is 45 MPH, so this truck is great for that type of driving. The brake booster runs on 12v. If it is not getting driven at high enough speed often enough (meaning the alternator is not spinning), could the 12v battery be getting depleted, causing the error lights and lack of brake booster? I'm not at home right now, so I can't put a meter on my battery to check the voltage, but I guess my basic question is, does the 12v battery have any way of getting charged if the engine isn't running?

 

A common cause seems to be NOT changing the factory DOT 3 moisture absorbing brake fluid on a regular basis. Brake fluid absorbs moisture and destroys the ABS pump/accumulator module etc. Everything on a GM hybrid two mode is concentrated in the ABS Assembly, it is a complicated electro hydraulic system with tiny interior valves / pump / accumulator and tiny orfices all built together as an assembly. If I had one that was acting out I would probably just go ahead and swap the entire abs assembly from a known good donor vehicle and flush the system thoroughly. Might be tempting to go with a DOT 5 synthetic brake fluid (I did not go to that extreme on my old beater ride). The DOT 5 fluid does not absorb moisture but costs a lot more than the standard DOT 3